Awesome

Table of Contents

• Table of Contents
• The latest news from ruby-lang.org
• Installation
  • How to install Ruby
    • Debian, Ubuntu
    • Windows Package Manager
    • macOS
    • Docker
    • Install rbenv with package managers
      • macOS
      • Debian, ubuntu and other derivatives
    • Install ruby with rbenv
    • Install ruby with RVM
  • How to install ruby gem manager, bundler gem
  • What is a Gemfile and Gemfile.lock
  • How to install a specific version of a particular ruby gem
  • How to update a single gem using Bundler
  • How to update every gem in the Gemfile using Bundler
• Introduction
• Reserved Words
• Comment
• Operators
  • Usage
  • Operator Precedence Table
• Variables and Scope
  • Local Variable
  • Instance Variable
  • Class Variable
  • Global Variable
  • Constant Variable
  • Pseudo variables
  • Pre-defined variables
  • Option variables
  • Pre-defined global constants
  • How to check scope of variables
• Conditional structures
  • if Modifier
  • If elsif else Statement
  • unless Statement
  • Case Statement
• Data types
  • How to check the data type
• Symbol
• String
  • String Interpolation
  • How to Extract a Substring
  • How to convert String to lower or upper case
  • Helpful methods
• Integer
  • Helpful methods
• Range
  • Helpful methods
  • How to use step with Range
• Methods
  • How to declare a method
  • How to call a method
  • How to define a default value for a method parameter
  • How to use another parameter for the default value
  • How to pass variable length argument to a method parameter
  • Modify object
  • Boolean method
  • Class method
• Blocks
  • How to check if a block is given
• Procs
• Lambdas
• Blocks VS Procs VS Lambdas
• Array
  • How to iterate an Array
    • each
    • each_with_index
    • each_with_object
    • each_index
    • map
    • collect
    • while
    • do while
    • for
    • until
    • times
    • upto
    • downto
    • step
    • inject
    • reduce
    • detect
    • find
    • select
    • reject
    • keep_if
    • delete_if
    • drop_while
    • reverse_each
  • Boolean Enumerable methods
    • all?
    • any?
    • one?
    • none?
    • empty?
  • Methods for combining
    • &
    • +
    • -
    • union
    • difference
    • product
  • How to check if a value exists in an Array (include?)
  • How to get array size
  • How to clear an Array
  • How to get the first element of an Array
  • How to get the last element of an Array
  • How to merge two Arrays
  • How to sort an Array
  • How to get the maximum from an Array
  • How to get Array elements using a range
  • How to get first n elements of an Array
  • How to access an element
  • How to remove one or more elements of an Array
  • How to remove duplicate elements from an Array
• Hash
  • How to group by count
  • What's the difference between Hash.new(0) and {}
  • How to sort a Hash
  • How to get the maximum from a Hash
  • Hash Built-in Methods
• Loop
  • while loop
  • for loop
  • do..while Loop
  • until Loop
  • How to break out from loop
  • How to skip inside a loop
  • How to repeat the current iteration
  • How to restart a loop
• Classes
  • How to inherit a class
  • How to check instance type
  • Print all method names of a class
  • Check if a Class has a particular method
• Modules
• Operator Overloading
• Exception Handling
• Regular expression
• Miscellaneous
  • How to generate random number
  • Check the syntax of a Ruby file
  • Concatenate String in a loop
  • CamelCase String split
  • Ruby scripts
• Platforms that supports Ruby
• Ruby frameworks
• My Ruby Articles
• Books and other resources
• Bug Reports and Feature Requests
• Contribution Guidelines
• Author
• License

The latest news from ruby-lang.org

• Ruby 3.4.0 rc1 Released <br/> _{2024-12-12 00:00:00}
• Ruby 3.3.6 Released <br/> _{2024-11-05 04:25:00}
• Ruby 3.2.6 Released <br/> _{2024-10-30 10:00:00}
• CVE-2024-49761: ReDoS vulnerability in REXML <br/> _{2024-10-28 03:00:00}
• Ruby 3.4.0 preview2 Released <br/> _{2024-10-07 00:00:00}
• Ruby 3.3.5 Released <br/> _{2024-09-03 06:40:00}
• CVE-2024-43398: DoS vulnerability in REXML <br/> _{2024-08-22 03:00:00}
• CVE-2024-41946: DoS vulnerability in REXML <br/> _{2024-08-01 03:00:00}
• CVE-2024-41123: DoS vulnerabilities in REXML <br/> _{2024-08-01 03:00:00}
• Ruby 3.2.5 Released <br/> _{2024-07-26 10:00:00}

Installation

How to install Ruby

First things first, make sure you have Ruby installed on your machine.

Debian, Ubuntu

Debian GNU/Linux and Ubuntu use the apt package manager. You can use it like this:

$ sudo apt-get install ruby-full

Windows Package Manager

On Windows, you can use the Windows Package Manager CLI to install Ruby:

> winget install RubyInstallerTeam.Ruby

macOS

Homebrew (macOS) Ruby versions 2.0 and above are included by default in macOS releases since at least El Capitan (10.11).

Homebrew is a commonly used package manager on macOS. Installing Ruby using Homebrew is easy:

$ brew install ruby

This should install the latest Ruby version.

List all the installed Ruby versions:

which -a ruby
# /usr/bin/ruby

Get information about currently used Ruby:

ruby -v
# ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.arm64e-darwin20]
gem env

Docker

In case you don’t want to install Ruby natively, you can use docker.

docker run -it --rm ruby:latest
# check which version of Ruby you're running
RUBY_VERSION

Run a specific version of Ruby.

docker run -it --rm ruby:2.7
# check which version of Ruby you're running
RUBY_VERSION

Install rbenv with package managers

rbenv is a version manager tool for the Ruby programming language on Unix-like systems. It is useful for switching between multiple Ruby versions on the same machine and for ensuring that each project you are working on always runs on the correct Ruby version.

rbenv

macOS

brew install rbenv ruby-build

Debian, ubuntu and other derivatives

sudo apt install rbenv

Load rbenv

# run this and follow the printed instructions:
rbenv init

Restart terminal for the changes to take effect.

Install ruby with rbenv

# list latest stable versions:
rbenv install -l

# list all local versions:
rbenv install -L

# install a Ruby version:
rbenv install 3.1.2

rbenv global 3.1.2   # set the default Ruby version for this machine
# or:
rbenv local 3.1.2    # set the Ruby version for this directory
rbenv local --unset

rbenv version # Displays the currently active Ruby version
=> 1.9.3-p327 (set by /Users/sam/.rbenv/version)

Install ruby with RVM

RVM allows you to install and manage multiple installations of Ruby on your system. It can also manage different gemsets. It is available for macOS, Linux, or other UNIX-like operating systems.

RVM

\curl -sSL https://get.rvm.io | bash -s stable
rvm list
rvm install 3.0.1
rvm list
rvm use 3.0.1

How to install ruby gem manager, bundler gem

# access the bash for executing the following commands
docker run -it --rm ruby:latest bash

gem install bundler
bundle -v
gem update bundler
gem uninstall bundler

Further reading

What is a Gemfile and Gemfile.lock

Gemfile is a configuration file for Bundler (also a gem), which contains a list of gems for your project (dependencies).

Further reading

# specify your gems in a Gemfile in your project’s root
ruby '2.5.6'

source 'https://rubygems.org'
gem 'nokogiri'
gem 'rack', '~>1.1'
gem 'rspec', :require => 'spec'

# install all the gems in the Gemfile
bundle install

How to install a specific version of a particular ruby gem

gem install bundler -v 1.17
gem install minitest -v 5.8.4

How to update a single gem using Bundler

bundle update nokogiri

Bundler attempted to update gem_name but its version stayed the same.

1. Another gem depends on the gem_name.
2. The version number is specified in your Gemfile for gem_name.

'gem_name', '~> 2.0.5'

How to update every gem in the Gemfile using Bundler

bundle update

Introduction

Ruby is a pure object-oriented and interpreted (executes the code at runtime) programming language invented in the mid-90s by Yukihiro Matsumoto. In Ruby, everything is an object. It is easy to learn with dynamic typing and automatic memory management.

With the idea that programming should be enjoyable for programmers, it was created to increase programmer productivity. It emphasizes the necessity for software to be understood by humans first and computers second.

Ruby will be quite familiar to Python, and Perl developers (and to a lesser extent C# and JavaScript developers) as Ruby was heavily inspired by Perl in certain areas (as was Python). Ruby is less related to languages like C, C++, or Java because these languages are compiled (not interpreted), statically typed, and focused on performance rather than flexibility and conciseness.

Ruby comes with a program that will show the results of any Ruby statements you feed it. Playing with Ruby code in interactive sessions like this is a terrific way to learn the language.

Open up IRB (which stands for Interactive Ruby).

• If you’re using macOS open up Terminal and type irb, then hit enter.
• If you’re using Linux, open up a shell and type irb and hit enter.
• If you’re using Windows, open Interactive Ruby from the Ruby section of your Start Menu.

1.next # 2

To test the above code, type the irb command from your shell to initiate the interpreter.

Reserved Words

Further reading

Comment

# single line comment

=begin
multiline
comment
=end

=begin Comment line 1 =end

puts "Hello world!"  # Inline comment about the code

We put a space between the contents of the comment & the start of the comment to make it easier to read.

I prefer # for multiline comments because it maintains my style guide and is easier to read.

Operators

Usage

# Addition
1 + 1   #=> 2

# Subtraction
2 - 1   #=> 1

# Multiplication
2 * 2   #=> 4

# Division
10 / 5  #=> 2
17 / 5    #=> 3, not 3.4
17 / 5.0  #=> 3.4

# Exponent
2 ** 2  #=> 4
3 ** 4  #=> 81

# Modulus (find the remainder of division)
8 % 2   #=> 0  (8 / 2 = 4; no remainder)
10 % 4  #=> 2  (10 / 4 = 2 with a remainder of 2)

a = 10
b = 20

a == b #=> false
a != b #=> true
a > b #=> false
a < b #=> true
a >= b #=> false
a <= b #=> true

# Comparison Operator
a <=> b #=> -1
c = 20
c <=> b #=> 0
c <=> a  #=> 1

# Used to test equality within a when clause of a case statement.
(1...10) === 5 #=> true

# True if the receiver and argument have both the same type and equal values.
1.eql?(1.0) #=> false

c = a + b  #=> 30
c += a #=> 40
c -= a #=> 30
c *= a #=> 300
c /= a #=> 30
c %= a #=> 3
c **= a #=> 59049

# Ruby Parallel Assignment

a = 10
b = 20
c = 30

a, b, c = 10, 20, 30

# Ruby Bitwise Operators

a = 60
b = 13
# & Binary AND Operator copies a bit to the result if it exists in both operands.

a & b #=> 12

# | Binary OR Operator copies a bit if it exists in either operand.

a | b #=> 61

# ^ Binary XOR Operator copies the bit if it is set in one operand but not both.

a ^ b #=> 49

# ~ Binary Ones Complement Operator is unary and has the effect of 'flipping' bits.

~a

# << Binary Left Shift Operator. The left operands value is moved
# left by the number of bits specified by the right operand.

a << 2

# >> Binary Right Shift Operator. The left operands value is moved
# right by the number of bits specified by the right operand.

a >> 2


# Ruby Logical Operators

a and b #=> true.
a or b #=> true.
a && b #=> true.
(a || b) #=> true.
!(a && b) #=> false.
not(a && b) #=> false.

# Ruby Ternary Operator

# ? :
# If Condition is true ? Then value X : Otherwise value Y
a == 10 ? puts 'Right' : puts 'Wrong'

# Ruby Range Operators

# .. Creates a range from start point to end point inclusive.
1..10 #=> Creates a range from 1 to 10 inclusive.

# ... Creates a range from start point to end point exclusive.
1...10 #=> Creates a range from 1 to 10 exclusive.

Operator Precedence Table

Variables and Scope

There are five different types of variables. The first character determines the scope.

Local Variable

Local variables are available to the block in which they are declared. A local variable declared within a loop or method cannot be accessed outside of that loop or method. They must either begin with an underscore or lowercase letter.

current_weather = "rainy"
_weather = "sunny"

Scope of a local variable is one of

• proc{ ... }
• loop{ ... }
• def ... end
• class ... end
• module ... end
• the entire program (unless one of the above applies)

Instance Variable

Instance variable is specific instance of an object. Changes to an instance variable are only available to that instance of the object. Instance variables are declared with a single @ sign.

@current_weather = "rainy"

Scope of an instance variable is

Instance variables cannot be altered except for some methods, and it's distinct to each object of a class.

Class Variable

Class variables are shared by all instances of a Ruby class. If one object instance changes the value of a class variable, that new value will essentially change for all other object instances. Class variables begin with a double @ sign.

@@current_weather = "rainy"

Scope of a class variable is one of

It can be called from a class by calling ClassName.class_variable, and it's independent of any object of a class.

Global Variable

Global variables in Ruby are accessible anywhere in the Ruby program, regardless of where they are declared. Global variable names must begin with a dollar sign ($).

The use of global variables is discouraged because they are visible anywhere in the code for a program and can be changed from anywhere in a program. This can make tracking down bugs extremely difficult.

$current_weather = "rainy"

Scope of a global variable is

It can be referred from anywhere in a program.

Constant Variable

Ruby constants are variables which, once assigned a value, shouldn't be changed. Constant declared outside of a class or module have global scope. If they are declared inside a class or module, they are available within the context of the class or module in which they were declared.

WEATHER = "rainy".freeze

Scope of a constant variable is

Accessible outside the class.

Pseudo variables

Pre-defined variables

Option variables

The variables which names are in the form of $-?, where ? is the option character, are called option variables and contains the information about interpreter command line options.

Source

Pre-defined global constants

Source

How to check scope of variables

defined? count
"local-variable"
defined? @id
"instance-variable"
defined? @@name
"class variable"
defined? $version
"global-variable"
defined? PI
"constant"

Conditional structures

if Modifier

num = 2
puts 'two' if num == 2

Executes code if the conditional is true.

If elsif else Statement

temp = 19

if temp >= 25
  puts "hot"
elsif temp < 25 && temp >= 18
  puts "normal"
else
  puts "cold"
end

# output
# normal

if expressions are used for conditional execution. The values false and nil are false, and everything else are true. Notice Ruby uses elsif, not else if nor elif.

Executes code if the conditional is true. If the conditional is not true, code specified in the else clause is executed.

An if expression's conditional is separated from code by the reserved word then, a newline, or a semicolon.

unless Statement

# The unless is opposite of if, evaluates when the statement is false

name = "rob"

# if name != "bob"
unless name == "bob"
  puts "hello stranger"
else
  puts "hello bob"
end
# output
# hello stranger

num = 6
puts 'not two' unless num == 2
# output
# not two

Executes code if conditional is false. If the conditional is true, code specified in the else clause is executed.

Case Statements

# case returns the value of the last expression executed

case input
# check an integer, 19
when 19
  puts "It's 19"
  # check a float number, 33.3
when 33.3
  puts "It's 33.3"
  # check an exact string, "Zaman"
when "Zaman"
  puts "Hi Zaman"
when 10
  puts "It's 10"
  # check against a range
when 7..11
  puts "It's between 7 and 11"
  # check against multiple values, "coffee"
when "tea", "coffee"
  puts "Happy days"
  # check against a regular expression, "aA6"
when /^a[A-Z]+[0-6]+$/
  puts "It's a valid match"
  # check any string by comparing against the String class, "any string"
when String
  puts "It's a String"
end

# using short syntax
case input
  when 19 then puts "It's 19"
end

# optional fallthrough
case input
  when 19 then puts "It's 19"
else
  puts "It's not 19"
end

# get the return value
marks = 86

result = case marks
         when 0..49 then "Fail"
         when 50..64 then "Pass"
         when 65..74 then "Credit"
         when 75..84 then "Distinction"
         when 85..100 then "High Distinction"
         else "Invalid marks"
         end

puts result
# High Distinction

Compares the expression specified by case and that specified by when using the === operator and executes the code of the when clause that matches.

The expression specified by the when clause is evaluated as the left operand. If no when clauses match, case executes the code of the else clause.

A when statement's expression is separated from code by the reserved word then, a newline, or a semicolon.

Data types

Data types represent different types of data such as numbers, booleans, strings, etc. As an object-oriented language, all data types are based on classes.

Further readings

Integer

In Ruby, Integer class is the basis for the two concrete classes that hold whole numbers. These concrete classes are Bignum and Fixnum. Fixnum holds integer values that are shown in the native machine word, whereas Bignum holds the integer value outside the range of Fixnum. Integer class contains a wide range of methods that are used for performing specified tasks. Integer class is a subclass of Numeric class.

Float

Float objects represent inexact real numbers using the native architecture's double-precision floating point representation.

String

A string is a group of letters that represent a sentence or a word. Strings are defined by enclosing a text within a single (') or double (") quotes. You can use both double quotes and single quotes to create strings. Strings are objects of class String. Double-quoted strings allow substitution and backslash notation but single-quoted strings doesn't allow substitution and allow backslash notation only for \ and \’.

Array

An array stores data or list of data. It can contain all types of data. Data in an array are separated by comma in between them and are enclosed within square bracket.The position of elements in an array starts with 0. A trailing comma is ignored.

Hash

A hash assign its values to its key. Value to a key is assigned by => sign. A key pair is separated with a comma between them and all the pairs are enclosed within curly braces. A hash in Ruby is like an object literal in JavaScript or an associative array in PHP. They’re made similarly to arrays. A trailing comma is ignored.

Boolean

Boolean data type represents only one bit of information either true or false.

Symbol

Symbols are light-weight strings. A symbol is preceded by a colon (:). They are used instead of strings because they can take up much less memory. Symbols have better performance.

How to check the data type

# both are synonymous
a = 37
a.kind_of? Integer
# true
a.is_a? Integer
# true

Symbol

Symbol objects represent names. Symbols are immutable, which means every symbol is unique, and we can't change it. Referencing the same symbol multiple times is the same as referencing the same object everywhere in your program. As a result, we can save both time and memory by referencing the same memory location. Symbols as hash keys.

week_days = {sunday: 11, monday: 222}

String

String Interpolation

String interpolation allows you to combine strings together:

name = "World"
puts "Hello #{name}"

puts "The total is #{1+1}"
# "the total is 2"

How to Extract a Substring

A substring is a smaller part of a string, it’s useful if you only want that specific part, like the beginning, middle, or end.

string = "abc123"
string[0,3]
# "abc"

string[3,3]
# "123"

string[0..-2]
# "abc12"

#remove or replace the substring
string[0..2] = ""
puts string
# "123"

How to convert String to lower or upper case

Helpful methods

Integer

Helpful methods

2.even?
# true
3.even?
# false
65.chr
#=> "A"
36.gcdlcm(60)
#=> [12, 180]
36.lcm(60)
#=> 180
(-12345).abs
#=> 12345
1.next
#=> 2
(-1).succ
#=> 0
1.pred
#=> 0
5.remainder(3)
#=> 2
12345.to_s
#=> "12345"
12345.to_s(2)
#=> "11000000111001"
12345.to_s(8)
#=> "30071"
12345.to_s(10)
#=> "12345"
12345.to_s(16)
#=> "3039"
12345.to_s(36)
#=> "9ix"
12345.digits
#=> [5, 4, 3, 2, 1]

Range

Ranges allow us to declare data with a beginning and an end, it has two operators to generate ranges.

# .. for creating inclusive ranges

range = 1..10
range.to_a
# output
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# ... for creating exclusive ranges

range = 1...10
range.to_a
# output
# [1, 2, 3, 4, 5, 6, 7, 8, 9]

Helpful methods

How to use step with Range

(1..20).step(2) { |number| puts "#{number}"}
# output
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

Methods

A method is a function that takes zero or more parameters and returns a value. Ruby method returns nil by default.

Method names should begin with a lowercase letter. If you begin a method name with an uppercase letter, Ruby might think that it is a constant and hence can parse the call incorrectly.

Methods should be defined before calling them, otherwise Ruby will raise an exception for undefined method invoking.

How to declare a method

In Ruby, the last statement evaluated is the return value of that method. The return statement is optional. Depending on your preference, you can choose either of them 👍. I prefer to use the return statement because it's easier to understand.

def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    parameter1 + parameter2
end

res = method_name(20, 10)
# output
# 30

def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    return parameter1 + parameter2
end
# output
# 30

How to call a method

res = method_name(parameter1, parameter2)
# In Ruby you can call methods without parentheses
res = method_name parameter1, parameter2

The most important drawback to using methods with parameters is that you need to remember the number of parameters whenever you call such methods. For example, if a method accepts three parameters and you pass only two, then Ruby displays an error.

How to define a default value for a method parameter

def method_name(parameter1, parameter2, type = "ADD")
  puts "#{parameter1} #{parameter2}"
  return parameter1 + parameter2 if type == "ADD"
  return parameter1 - parameter2 if type == "SUB"
end

res = method_name(20, 10)
# output
# 30

How to use another parameter for the default value

def method_name(num1, num2 = num1)
  return num1 + num2
end

res = method_name(10)
# output
# 20

How to pass variable length argument to a method parameter

def method_name(type, *values)
  return values.reduce(:+) if type == "ADD"
  return values.reduce(:-) if type == "SUB"
end

numbers = [2, 2, 2, 3, 3, 3]

res = method_name("ADD", *numbers)
# output
# 15

res = method_name("SUB", *numbers)
# output
# -11

# or you can provide the values like this
res = method_name("ADD", 2, 2, 2, 3, 3, 3)
# output
# 15

Modify object

The ! is used after the method when you want to modify the object.

a = ["Drama",
"Mystery",
"Crime",
"Sci-fi",
"Disaster",
"Thriller"]
a.sort
puts a
# we didn't modify the object
# Drama
# Mystery
# Crime
# Sci-fi
# Disaster
# Thriller

a.sort!
puts a
# modify the object
# Crime
# Disaster
# Drama
# Mystery
# Sci-fi
# Thriller

Boolean method

In ruby methods that end with a question mark (?) are called boolean methods, which either returns true or false.

"some text".nil?
# false
nil.nil?
# true

You can have your own boolean methods.

def is_vowel?(char)
  ['a','e','i','o','u'].include? char
end

is_vowel? 'a'
# true
is_vowel? 'b'
# false

Class method

A class method is a class-level method. There are multiple ways of defining a class method.

When a method is defined outside of the class definition, the method is marked as private by default. On the other hand, the methods defined in the class definition are marked as public by default. The default visibility and the private mark of the methods can be changed by public or private of the Module.

Whenever you want to access a method of a class, you first need to instantiate the class. Then, using the object, you can access any member of the class.

Ruby gives you a way to access a method without instantiating a class. Let us see how a class method is declared and accessed −

class Mobile
  def self.ring
    "ring ring ring..."
  end
end

Mobile.ring

class Mobile
  def Mobile.ring
    "ring ring ring..."
  end
end

Mobile.ring

class Mobile
  class << self
    def ring
      "ring ring ring..."
    end
  end
end

Mobile.ring

To access this method, you need not create objects of the class Mobile.

A class method is an instance method of the class object. When a new class is created, an object of type Class is initialized and assigned to a global constant (Mobile in this case).

Mobile = Class.new do
  def self.ring
    "ring ring ring..."
  end
end

Mobile.ring

Mobile = Class.new

class << Mobile
  def ring
      "ring ring ring..."
  end
end

Mobile.ring

Blocks

In Ruby, a block is a piece of code that can be passed as an argument to a method, and is executed by the method at a later time. Blocks are defined using the keywords "do" and "end" or using curly braces {}. They can also be passed using the "yield" keyword within a method. They are commonly used in iterators such as "each" and "map" to perform an operation on each element of a collection. A block returns the last evaluated statement.

Blocks in Ruby have a few key aspects that are significant:

1. Block can accept arguments and returns a value.
2. Block does not have their own name.
3. Block consist of chunks of code.
4. A block is always invoked with a function or can say passed to a method call.
5. To call a block within a method with a value, yield statement is used.
6. Blocks can be called just like methods from inside the method that it is passed to.

# return value
def give_me_data
  data = yield
  puts "data = #{data}"
end

give_me_data { "Big data" }

# output
# data = Big data

# single line block
salary = [399, 234, 566, 533, 233]
salary.each { |s| puts s }

# puts s = block body
# |s| = block arugments

# multiline block
salary.each do |s|
  a = 10
  res = a * s
  puts res
end

# block body
# a = 10
# res = a * s
# puts res

# block arugments
# |s|

Methods can take blocks implicitly and explicitly. If you want to call a block implicitly use the yield keyword. Yield finds the block and calls the passed block. Since you can pass implicit blocks, you don't have to call yield, and the block will be ignored.

# passing a block implicitly
def give_me_data
  puts "I am inside give_me_data method"
  yield
  puts "I am back in give_me_data method"
end

give_me_data { puts "Big data" }

# output
# I am inside give_me_data method
# Big data
# I am back in give_me_data method

# call multiple times
def give_me_data
  yield
  yield
  yield
end

give_me_data { puts "Big data" }

# output
# Big data
# Big data
# Big data

# call with block arguments

def give_me_data
  yield 10
  yield 100
  yield 30
end

give_me_data { |data| puts "Big data #{data} TB" }

# output
# Big data 10 TB
# Big data 100 TB
# Big data 30 TB

# call with multiple block arguments

def give_me_data
  yield "Big data", 10, "TB"
  yield "Big data", 100, "GB"
  yield "Big data", 30, "MB"
end

give_me_data { |text, data, unit| puts "#{text} #{data} #{unit}" }

# output
# Big data 10 TB
# Big data 100 GB
# Big data 30 MB

#  block will try to return from the current context
give_me_data
  puts "I am inside give_me_data method"
end

def test
  puts "I am inside test method"
  give_me_data { return 10 } # code returns from here
  puts "I am back in test method"
end

return_value = test

# output
# I am inside test method
# I am inside give_me_data method
# 10

# passing a block explicitly by using an ampersand parameter, here we are explicitly defining the method with block parameter and calling it
def give_me_data(&block)
  block.call
  block.call
end

give_me_data { puts "Big data" }

# output
# Big data
# Big data

How to check if a block is given

Block parameter is mandatory when you call yield inside a method; otherwise, it will raise an exception

def give_me_data
  yield
end

give_me_data

# output
# LocalJumpError: no block given (yield)

# you can use block_given? method to handle the exception and make the block optional

def give_me_data
  return "no block" unless block_given?
  yield
end

give_me_data { puts "Big data" }
give_me_data

# output
# Big data

def give_me_data(&block)
  block.call if block
end

give_me_data { puts "Big data" }
give_me_data

# output
# Big data

Procs

In Ruby, a proc (short for "procedure") is a way to package a block of code as an object, which can be passed around and reused like any other object in Ruby. This allows you to define a block of code once and use it in multiple places, rather than having to repeat the same code multiple times.

The benefits of using Procs include:

• Reus-ability: Since a Proc is an object, it can be stored in a variable and passed as an argument to a method, allowing it to be used in multiple places throughout your code.
• Flexibility: Procs can be used in a variety of situations where a block is accepted, such as in iterators, callbacks, and event handlers.
• Clarity: Procs can help to make your code more readable by encapsulating complex logic into a single, named object that can be easily understood.

Procs can be created by passing a block to the Proc.new or lambda methods, or by using the shorthand notation: my_proc = proc {puts "Hello, World!"} and my_proc.call can be used to invoke the proc

p = Proc.new { puts "Hello World" }

def give_me_data(proc)
  proc.call
end

give_me_data p

# output
# Hello World

# arbitrary arguments
p = Proc.new { |count| "Hello World " * count }

def give_me_data(proc)
  proc.call 5, 2
end

give_me_data p

# output
# "Hello World Hello World Hello World Hello World Hello World "

#  proc will try to return from the current context
p = Proc.new { return 10 }
p.call

# output
LocalJumpError: unexpected return

# because you can’t return from the top-level context

def give_me_data
  puts "I am inside give_me_data method"
  p = Proc.new { return 10 }
  p.call # code returns from here
  puts "I am back in give_me_data method"
end

return_value = give_me_data
puts return_value

# output
# I am inside give_me_data method
# 10

Lambdas

Lambdas are a powerful feature of the Ruby language. They allow you to wrap logic and data into a portable package. A lambda function encapsulates control flow, parameters and local variables into a single package assigned to a variable or used inline. If assigned to a variable, it can be passed to other functions or stored in data structures, just like a more typical variable containing a string or float.

A lambda function can then be executed far from the code location where it was defined. Lambda functions are often called anonymous functions or a function literal, wrap the lambda with do and end (for multiline) or curly brackets { and } (for a single line). Lambda returns the last evaluated statement.

With Ruby, the lambda keyword is used to create a lambda function. It requires a block and can define zero or more parameters. You call the resulting lambda function by using the call method.

The following are specific situations in which you might want to use a Ruby lambda.

1. Encapsulating complicated logic
2. An in-memory state machine or data pipeline
3. Perfect for simple callbacks
4. Used in ActiveRecord scopes

In Ruby, a lambda is a type of Proc that has some specific characteristics and behaviors. Like a Proc, a lambda is a way to package a block of code as a object that can be passed around and reused, but there are some differences between the two.

The main difference between a lambda and a proc is in the way they handle the "return" keyword. In a proc, the "return" keyword will return from the method that the proc was defined in, whereas in a lambda, the "return" keyword will only return from the lambda itself.

The benefits of using a lambda include:

• Clarity: Like procs, using a lambda can help to make your code more readable by encapsulating complex logic into a single, named object that can be easily understood.
• Strictness: Since Lambdas are more strict in terms of how they handle the return keyword, it can be beneficial in cases where you want to ensure that a block of code behaves in a specific way.
• Strict number of arguments: Lambdas also check the number of arguments passed to them, unlike procs which don't check the number of arguments passed to them.

# there are multiple ways to declare a lambda
l = lambda { puts "Hello World" }
# shorthand
l = -> { puts "Hello World" }

# call the lambda
l.call

# output
# Hello World

# there are multiple ways you can call a lambda
l.()
l[]

# strict arguments
l = -> (count) { "Hello World " * count }
l.call 5

# output
# "Hello World Hello World Hello World Hello World Hello World "

l.call 5, 2

# output
wrong number of arguments (given 2, expected 1)

# lambdas return from the lambda itself, like a regular method
l = -> { return 10 }
l.call

# output
# 10

def give_me_data
  puts "I am inside give_me_data method"
  l = -> { return 10 }
  l.call
  puts "I am back in give_me_data method"
end

return_value = give_me_data
puts return_value

# output
# I am inside give_me_data method
# I am back in give_me_data method
# nil # because puts return nil

In summary, procs are more flexible and forgiving in their behavior, while lambdas are more strict and predictable. It depends on the specific use-case and the desired behavior of the code.

Blocks VS Procs VS Lambdas

All of them are used for executing a single line or multiline code.

Array

Unlike other programming languages like Java, Ruby only has dynamic arrays but no static arrays. That means you don’t have to worry about the size of the array while adding new values.

One way Ruby allows you to represent a collection of data is with arrays, which you can think of as ordered lists. Rather than working with individual variables, numbers, or strings, an array allows you to create and manipulate an ordered and indexed collection of these data.

The individual variables, numbers, or strings within an array are known as elements.

An array can contain any combination of variables, numbers, strings, or other Ruby objects (including other arrays), although it is advisable to keep similar data types in any one array.

There are multiple ways we can initialize an empty array.

array = Array.new   #=> []
# or
array = []

# An Array can contain different types of objects.
array = [1, "two", 3.0] #=> [1, "two", 3.0]

Fill an array with the initial size and a default object.

numbers = Array.new(3)            #=> [nil, nil, nil]
numbers = Array.new(3, 7)         #=> [7, 7, 7]
numbers = Array.new(3, true)      #=> [true, true, true]

numbers = []
numbers.fill(7, 0..2)   #=> [7, 7, 7]

How about an array with different hashes? No problem, Ruby has you covered!

array_with_hashes = Array.new(2) { {} } #=> [{}, {}]
array_with_hashes[0][:name] = "Bob"
array_with_hashes[0][:id] = 10          #=> [{:name=>"Bob", :id=>10}, {}]

Let’s talk about 2D arrays briefly.

temperature_data = [
                     ["A908", 38],
                     ["A909", 37],
                     ["A910", 38],
                   ]
temperature_data[0]    #=> ["A908", 38]
temperature_data[0][0] #=> "A908"
temperature_data[0][1] #=> 38

Array indexing starts at 0. A negative index is relative to the end of the array, so -1 is the last element of the array, -2 is the second last element in the array, and so on.

str_array = ["This", "is", "a", "small", "array"]
str_array[0]            #=> "This"
str_array[1]            #=> "is"
str_array[4]            #=> "array"

# A negative index is an offset, backwards, from the end of the array:

# Index -1 indicates the last element.
str_array[-1]             #=> "array"

# Index -2 indicates the next-to-last element.
str_array[-2]             #=> "small"

# A negative index is in range if its absolute value is
# not larger than the size of the array.

str_array[-6]             #=> nil

# str_array.at
puts str_array.at(0)      #=> "This"

arr = [1, 2, 3, 4, 5, 6]
arr[100]                  #=> nil
arr[-3]                   #=> 4
arr[2, 3]                 #=> [3, 4, 5]
arr[1..4]                 #=> [2, 3, 4, 5]
arr[1..-3]                #=> [2, 3, 4]

# To raise an error for indices outside of the array bounds
# or else to provide a default value when that happens, you can use fetch.

arr = ['a', 'b', 'c', 'd', 'e', 'f']
arr.fetch(100)            #=> IndexError: index 100 outside of array bounds: -6...6
arr.fetch(100, "oops")    #=> "oops"


arr = [1, 2, 3, 4, 5, 6]

# The special methods first and last will return the first and last elements of an array
arr.first                #=> 1
arr.last                 #=> 6

# To return the first n elements of an array, use take
arr.take(3)             #=> [1, 2, 3]

# drop does the opposite of take, by returning the elements
# after n elements have been dropped
arr.drop(3)            #=> [4, 5, 6]

Add values at the end of the array.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.push(11)          #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
numbers.push(12, 13, 14)  #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

Remove value from the end of the array.

num_array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
num_array.pop             #=> 10
num_array                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Add values at the start of the array.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(0)          #=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(-3, -2, -1) #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

To retrieve and at the same time remove the first item, use shift:

numbers.shift #=> 1
numbers       #=> [2, 3, 4, 5, 6, 7, 8, 9, 10]

To delete an element at a particular index:

numbers.delete_at(2) #=> 4
numbers              #=> [2, 3, 5, 6, 7, 8, 9, 10]

To delete a particular element anywhere in an array, use delete:

numbers.delete(2) #=> 2
numbers           #=> [3, 5, 6, 7, 8, 9, 10]

Insert values at the given index.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.insert(0, 0)           #=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.insert(0, -3, -2, -1)  #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.insert(-1, 12, 13, 14) #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14]
numbers.insert(-4, 11)         #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

How about a block to populate the values of an array?

numbers = Array.new(10) { |n| n = n * 2 } #=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

It gets easier to fill an array.

numbers = Array(100..110) #=> [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]

# or we can convert a range to an array
(100..110).to_a #=> [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]

A useful method if you need to remove nil values from an array is compact:

arr = ['foo', 0, nil, 'bar', 7, 'baz', nil]
arr.compact  #=> ['foo', 0, 'bar', 7, 'baz']
arr          #=> ['foo', 0, nil, 'bar', 7, 'baz', nil]
arr.compact! #=> ['foo', 0, 'bar', 7, 'baz']
arr          #=> ['foo', 0, 'bar', 7, 'baz']

Another common need is to remove duplicate elements from an array.

It has the non-destructive uniq, and destructive method uniq!

arr = [2, 5, 6, 556, 6, 6, 8, 9, 0, 123, 556]
arr.uniq #=> [2, 5, 6, 556, 8, 9, 0, 123]

How to iterate an Array

There are multiple ways you can iterate an Array.

each

# when you have single line block
salary = [399, 234, 566, 533, 233]
salary.each { |s| puts s }
# output
# 399
# 234
# 566
# 533
# 233

# when you have a multiline block, you can replace the curly brackets {} with do and end
salary.each do |s|
  a = 10
  res = a * s
  puts res
end
# output
# 3990
# 2340
# 5660
# 5330
# 2330

# or you can do the same thing just using curly brackets {} and semicolons as separators instead of new lines
salary.each { |s| a = 10 ; res = a * s ; puts res }

each_with_index

salary = [399, 234, 566, 533, 233]
salary.each_with_index { |value, index| puts "#{index} #{value}" }
# output
# 0 399
# 1 234
# 2 566
# 3 533
# 4 233

each_with_object

colors = [{color: "red", count: 3}, {color: "red", count: 5}, {color: "black", count: 4}]
colors.each_with_object(Hash.new(0)) { |color, hash| hash["color_"+color[:color]] = color[:color].upcase; hash["count_"+color[:color]] += color[:count] }
# output
{"color_red"=>"RED", "count_red"=>8, "color_black"=>"BLACK", "count_black"=>4}

[1, 2, 3].each_with_object(0) { |number, sum| sum += number}
# output
# 0
# because 0 is immutable, since the initial object is 0, the method returns 0

each_index

salary = [399, 234, 566, 533, 233]
salary.each_index { |i| puts i}
# output
# 0
# 1
# 2
# 3
# 4

map

salary = [399, 234, 566, 533, 233]
salary.map { |s|  s * 10  }
# returns
# [3990, 2340, 5660, 5330, 2330]

# on the other hand each returns the originl values
salary = [399, 234, 566, 533, 233]
salary.each { |s|  s * 10  }
# returns
# [399, 234, 566, 533, 233]

collect

salary = [399, 234, 566, 533, 233]
salary.collect { |s| s > 400 }
# output
# [false, false, true, true, false]

while

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
while index < planets.size
  puts "#{planets[index]}"
  index += 1
end

a = 1
star = '*'
while a <= 10
  puts star
  star += '*'
  a += 1
end

do while

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
loop do
  puts "#{planets[index]}"
  index += 1
  break if planets[index] == "Mars" or index > planets.size
end

for

for value in [2, 3, 5, 7]
  puts value
end

until

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = planets.size - 1
until index < 0
  puts "#{planets[index]}"
  index -= 1
end

a = 1
star = '*'
until star.length > 10
  puts star
  star += '*'
  a += 1
end

times

10.times { puts "#{rand(1..100)}"}
# output
# will print 10 random numbers

# just because you can doesn't mean you should iterate an array like this
data_sample = [2, 3, 5, 7]
data_sample.size.times { |index| puts "#{data_sample[index]}" }
# output
# 2
# 3
# 5
# 7

upto

data_sample = [2, 3, 5, 7]
0.upto((data_sample.size - 1) / 2) { |index| puts "#{data_sample[index]}" }
# output
# 2
# 3

downto

data_sample = [2, 3, 5, 7]
(data_sample.size - 1).downto(data_sample.size / 2) { |index| puts "#{data_sample[index]}" }
# output
# 7
# 5

step

1.step(20, 2) { |number| puts "#{number}"}
# output
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

19.step(1, -2) { |number| puts "#{number}"}
# output
# 19
# 17
# 15
# 13
# 11
# 9
# 7
# 5
# 3
# 1

inject

numbers = [2, 2, 2, 2, 2]
numbers.inject{ |res, n| res + n }
# output is the result of the sum of all numbers
# if you do not set an initial value for res, then the first element of the array is used as the initial value of res
# 10

# now set the value of res with 11
numbers = [2, 2, 2, 2, 2]
numbers.inject(11) { |res, n| res + n }
# so 11 + 2, 13 + 2, 15 + 2, 17 + 2 and 19 + 2
# 21

# using symbol
numbers = [2, 2, 2, 2, 2]
numbers.inject(:+)
# output
# 10

# using initial value and a symbol
numbers = [2, 2, 2, 2, 2]
numbers.inject(11, :+)
# output
# 21

reduce

numbers = [2, 2, 2, 2, 2]
numbers.reduce(11, :+)
# output
# 21

detect

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.detect { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth

salary = [399, 234, 566, 533, 233]
salary.detect { |s| s > 1000 }
# output
# nil

find

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.find { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth

select

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.select { |n| n % 2 == 0 }
# now you have an array of even numbers, how cool is that
# [2, 4, 6, 8, 10]
# returns an empty array if there is no value that satisfy your logic
[1, 1, 1].select { |n| n % 2 == 0 }
# no even numbers
# []

reject

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.reject { |n| n % 2 == 0 }
# reject if the number is even, so now we have an array of odd numbers
# [1, 3, 5, 7, 9]

keep_if

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.keep_if { |n| n % 2 == 0 }
# numbers array holds only even numbers
# [2, 4, 6, 8, 10]

delete_if

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.delete_if { |n| n % 2 == 0 }
# numbers array holds only odd numbers
# [1, 3, 5, 7, 9]

drop_while

numbers = [1, 2, 3, 1, 2, 3, 0]
numbers.drop_while { |n| n < 3 }
# is 3 less than 3, returns false, so drop 1, 2
# [3, 1, 2, 3, 0]

reverse_each

words = %w[first second third fourth fifth sixth]
str = ""
words.reverse_each {|word| str += "#{word} "}
p str #=> "sixth fifth fourth third second first "

Boolean Enumerable methods

all?

[2, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# true
[1, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# false

any?

[1, 3, 5, 7, 10].any? { |num| num % 2 == 0 }
# true
[1, 3, 5, 7, 19].any? { |num| num % 2 == 0 }
# false

one?

[1, 3, 2, 5, 7].one? { |num| num % 2 == 0 }
# true
[1, 3, 2, 5, 4].one? { |num| num % 2 == 0 }
# false

none?

[1, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# true
[2, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# false

empty?

[].empty?
# true
[1, 3, 5, 7, 9].empty?
# false

Methods for combining

&

[0, 1, 2, 3] & [1, 2] # => [1, 2]
[0, 1, 0, 1] & [0, 1] # => [0, 1]

intersection

[0, 1, 2, 3].intersection([0, 1, 2], [0, 1, 3]) # => [0, 1]
[0, 0, 1, 1, 2, 3].intersection([0, 1, 2], [0, 1, 3]) # => [0, 1]

+

a = [0, 1] + [2, 3]
a # => [0, 1, 2, 3]

-

[0, 1, 1, 2, 1, 1, 3, 1, 1] - [1] # => [0, 2, 3]
[0, 1, 2, 3] - [3, 0] # => [1, 2]
[0, 1, 2] - [4] # => [0, 1, 2]

union

[0, 1, 2, 3].union([4, 5], [6, 7]) # => [0, 1, 2, 3, 4, 5, 6, 7]
[0, 1, 1].union([2, 1], [3, 1]) # => [0, 1, 2, 3]
[0, 1, 2, 3].union([3, 2], [1, 0]) # => [0, 1, 2, 3]

difference

[0, 1, 1, 2, 1, 1, 3, 1, 1].difference([1]) # => [0, 2, 3]
[0, 1, 2, 3].difference([3, 0], [1, 3]) # => [2]
[0, 1, 2].difference([4]) # => [0, 1, 2]

product

a = [0, 1, 2]
a1 = [3, 4]
p = a.product(a1)
p.size # => 6 # a.size * a1.size
p # => [[0, 3], [0, 4], [1, 3], [1, 4], [2, 3], [2, 4]]

How to check if a value exists in an Array (include?)

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.include? "Mars"
# output
# true

planets.include? "Pluto"
# output
# false

How to get array size

# you can either use size or length, both are synonymous
planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.size
# output
# 8

planets.length
# output
# 8

How to clear an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.clear
# output
# []

How to get the first element of an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[0]
# or
numbers.first
# output
# 1

How to get the last element of an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[-1]
# or
numbers.last
# output
# 10

How to merge two Arrays

a = ["tom", "mot", "otm"]
b = [2, 3, 5]

a.zip(b)

# outout
# [["tom", 2], ["mot", 3], ["otm", 5]]

How to sort an Array

primes = [7, 2, 3, 5]
sorted_primes = primes.sort
puts "#{sorted_primes}"
# output
# [2, 3, 5, 7]

or in-place sort

primes = [7, 2, 3, 5]
primes.sort!
puts "#{primes}"
# output
# [2, 3, 5, 7]

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.sort
# output
# ["Earth", "Jupiter", "Mars", "Mercury", "Neptune", "Saturn", "Uranus", "Venus"]

planets.sort_by { |p| p }
# output
# ["Earth", "Jupiter", "Mars", "Mercury", "Neptune", "Saturn", "Uranus", "Venus"]

planets.sort_by { |p| p.length }
# output
# ["Mars", "Earth", "Venus", "Saturn", "Uranus", "Neptune", "Jupiter", "Mercury"]

How to get the maximum from an Array

primes = [7, 2, 3, 5]
primes.max_by { |p| p }
# output
# 7

How to get Array elements using a range

# numbers[start..end], both index are inclusive
puts numbers[0..3]
# 1
# 2
# 3
# 4

# numbers[start..end], end index is exclusive
puts numbers[0...3]
# 1
# 2
# 3

# or numbers[start..length]
puts numbers[0, 1]
# 1

How to get first n elements of an Array

primes = [7, 2, 3, 5]
primes.take(3)
# [7, 2, 3]

How to access an element

primes = [7, 2, 3, 5]
primes.fetch(3)
# 5
# Fetch will throw an error if the element does not exist
primes.fetch(10)
# (index 10 outside of array bounds: -4...4)
# or get an default value
primes.fetch(10, -1)
# -1

How to remove one or more elements of an Array

Remove first n elements.

primes = [7, 2, 3, 5]
primes.drop(3)
# [5]

Remove first element.

primes = [7, 2, 3, 5]
primes.shift
# [2, 3, 5]

Remove last element.

primes = [7, 2, 3, 5]
primes.pop
# [7, 2, 3]

Remove element with an Index.

primes = [7, 2, 3, 5]
primes.delete_at(-1)
# [7, 2, 3]

Remove all occurrences of an element.

primes = [7, 2, 3, 5, 5]
primes.delete(5)
# [7, 2, 3]

How to remove duplicate elements from an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 1]
numbers.uniq
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Hash

A Hash maps each of its unique keys to a specific value. But it has certain similarities to an Array, but an Array index is always an Integer. A Hash key can be (almost) any object.

Let's start with some basic operations. Below we have an example of how to initialize an empty hash.

students = Hash.new
or
students = {}

Here we have an empty hash, without any key-value pairs. Now the question is, what if someone wants to access a key that does not exist in the hash? Well, the answer is nil, which is the default value.

puts "#{students[:name]}"
# nil

Let’s add some values to the hash using symbols. There are two ways to declare symbols as keys.

students = Hash.new
students = { name: 'John', email: 'john@col.com' }
puts "#{students[:name]}"
# or
students = Hash.new
students = { :name => 'John', :email => 'john@col.com' }
puts "#{students[:name]}"

I prefer the former one because I’ve to type less! How about initializing with default values, here we have initialized an empty hash with a default value of “no email” for every key.

students = Hash.new("no data")
puts "#{students[:email]}"
# no email
# or
students = Hash.new
students.default = "no data"
puts "#{students[:email]}"
# no email

The Hash.new() creates a single default object for every key. That’s why by altering it for one key changes for other keys as well. For example, when we change the default value for the key id, it affects other unassigned key’s default value, in this case, name.

students = Hash.new("no data")
students[:email] = "john@col.com"
puts "#{students[:email]}"
# john@col.com
puts "#{students[:id]}"
# no data
puts "#{students[:name]}"
# no data
students[:id].upcase!
puts "#{students[:email]}"
# john@col.com
puts "#{students[:id]}"
# NO DATA
puts "#{students[:name]}"
# NO DATA

If the above code behavior is not desired, you can use Hash.new {|hash, key| block } instead. This method creates a default object each time for different keys.

students = Hash.new {|hash, key| hash[key] = "no data" }
students[:email] = "john@col.com"
puts "#{students[:email]}"
# john@col.com
puts "#{students[:id]}"
# no data
puts "#{students[:name]}"
# no data
students[:id].upcase!
puts "#{students[:email]}"
# john@col.com
puts "#{students[:id]}"
# NO DATA
puts "#{students[:name]}"
# no data

In short, Hash.new(some_value) sets a default value of some_value for every key that does not exist in the hash, Hash.new {|hash, key| block } creates a new default object for every key that does not exist in the hash, and Hash.new() or {} sets nil for every key.

How to group by count

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
freq_hash = numbers.each_with_object(Hash.new(0)) { |number, hash| hash[number] += 1 }
puts "#{freq_hash}"
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

or

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
freq_hash = Hash.new(0)
numbers.each { |number| freq_hash[number] += 1 }
puts "#{freq_hash}"
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

or from Ruby 2.7+

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
numbers.tally
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

What's the difference between Hash.new(0) and {}

# Hash.new(0) sets a default value of 0 for every key that do not exist in the hash.
# {} or Hash.new() sets nil for every key

h1 = Hash.new(0)
h1[:count] += 1
puts "#{h1[:count]}"
# output
# 1

puts "#{h1[:new_key]}"
# output
# 0

h2 = {}
h2[:count] += 1
# error
"undefined method `+` for nil:NilClass"

How to sort a Hash

hash = {e: 2, d: 3, c: 5, b: 7, a: 11}
hash.sort
# output
# [[:a, 11], [:b, 7], [:c, 5], [:d, 3], [:e, 2]]

hash.sort_by { |k, v| k }
# output
# [[:a, 11], [:b, 7], [:c, 5], [:d, 3], [:e, 2]]

hash.sort_by { |k, v| v }
# output
# [[:e, 2], [:d, 3], [:c, 5], [:b, 7], [:a, 11]]

How to get the maximum from a Hash

hash = {e: 2, d: 3, c: 5, b: 7, a: 11}
hash.max_by { |k, v| v }
# output
# [:a, 11]

Hash Built-in Methods

Loop

The loops in Ruby are :

1. while loop
2. for loop
3. do..while loop
4. until loop

while loop

The condition which is to be tested, given at the beginning of the loop and all statements are executed until the given boolean condition satisfies. When the condition becomes false, the control will be out from the while loop. It is also known as Entry Controlled Loop because the condition to be tested is present at the beginning of the loop body. So basically, while loop is used when the number of iterations is not fixed in a program.

# Ruby program to illustrate 'while' loop

# variable count
count = 4

# using while loop
# here conditional is count i.e. 4
while count >= 1

  # statements to be executed
  puts "Ruby Cheatsheet"
  count = count - 1

  # while loop ends here
end

Output

Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet

for loop

“for” loop has similar functionality as while loop but with different syntax. for loop is preferred when the number of times loop statements are to be executed is known beforehand. It iterates over a specific range of numbers. It is also known as Entry Controlled Loop because the condition to be tested is present at the beginning of the loop body.

# Ruby program to illustrate 'for'
# loop using range as expression

text = "Ruby Cheatsheet"

# using for loop with the range
for count in 1..5 do

  puts text

end

Output

Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet
Ruby Cheatsheet

do..while Loop

do while loop is similar to while loop with the only difference that it checks the condition after executing the statements, i.e it will execute the loop body one time for sure. It is a Exit-Controlled loop because it tests the condition which presents at the end of the loop body.

# Ruby program to illustrate 'do..while'loop

# starting of do..while loop
loop do

  puts "Ruby Cheatsheet"

  val = '7'

  # using boolean expressions
  if val == '7'
    break
  end

  # ending of ruby do..while loop
end

Output

Ruby Cheatsheet

until Loop

Ruby until loop will executes the statements or code till the given condition evaluates to true. Basically it’s just opposite to the while loop which executes until the given condition evaluates to false. An until statement’s conditional is separated from code by the reserved word do, a newline, or a semicolon.

var = 7

# using until loop
# here do is optional
until var == 11 do

  # code to be executed
  puts var * 10
  var = var + 1

  # here loop ends
end

Output

70
80
90
100

How to break out from loop

break terminates the most internal loop. Terminates a method with an associated block if called within the block (with the method returning nil).

# by using break keyword
salary = [399, 234, 566, 533, 233]
salary.each do |s|
  break if s == 566

  puts s
end
#output
# 399
# 234

How to skip inside a loop

# by using next keyword
salary = [399, 234, 566, 533, 233]
salary.each do |s|
  next if s == 533

  puts s
end
# output
# 399
# 234
# 566
# 233

How to repeat the current iteration

data = [456, 3000]
retry_count = 0
status = "network failure"
sum = 0
data.each do |d|
    if retry_count == 3
        status = "connection established"
        retry_count = 0
        redo
    elsif status == "network failure" and retry_count < 5
        puts "network failure #{retry_count}"
        retry_count += 1
        redo
    elsif status == "connection established"
        puts d
        sum += d
    end
end

# output of sum
# 3456

How to restart a loop

numbers = [2, 2, 44, 44]
sum = 0
begin
    numbers.each do |s|
        if rand(1..10) == 5
            puts "hi 5, let's do it again!"
            sum = 0
            raise "hi 5"
        end
        puts s
        sum += s
    end
rescue
    retry
end

Classes

class Person
    # when you create a new object, it looks for a method named initialize and executes it, like a constructor in java
    # def initialize(name, number)
    #    @name = name
    #    @number = number
    # end

    # instance variable
    # @name

    # class variable
    # @@count

    # attr_accessor acts as a getter and setter for the following instance attributes
    attr_accessor :name, :number

    # class variable must be initialized
    @@count = 0

    def self.count
        @@count
    end

    def self.count=(count)
        @@count = count
    end

    def initialize
        @@count += 1
    end
end

# create an instance of the Person class
p1 = Person.new

# set attributes of the Person class
p1.name = "Yukihiro Matsumoto"
p1.number = 9999999999

# get attributes of the Person class
puts "#{p1.name}"
puts "#{p1.number}"
puts "#{Person.count}"

# Yukihiro Matsumoto
# 9999999999
# 1

p2 = Person.new
p2.name = "Yukihiro Matsumoto"
p2.number = 9999999999

# get attributes of the Person class
puts "#{p2.name}"
puts "#{p2.number}"
puts "#{Person.count}"

# Yukihiro Matsumoto
# 9999999999
# 2

# set class variable
Person.count = 3
puts "#{Person.count}"
# 3

How to inherit a class

class Person
    attr_accessor :name, :number
end

# use < symbol to inherit methods and attributes from the parent class
class Student < Person
    attr_accessor :id
end

s = Student.new

s.name = "James Bond"
s.number = 700
s.id = 678

puts "#{s.name}"
James Bond

puts "#{s.number}"
700

puts "#{s.id}"
678

How to check instance type

# Returns true if the object is an instance of the given class, not a subclass or superclass
class Vehicle; end
class Car < Vehicle; end
class Audi < Car; end

car = Car.new
car.instance_of? Vehicle
false
car.instance_of? Car
true
car.instance_of? Audi
false

a = 7
a.instance_of? Integer
true
a.instance_of? Numeric
false

Print all method names of a class

puts (String.methods).sort
# Exclude methods that are inherited from Object class
puts (String.methods - Object.public_instance_methods).sort

Check if a Class has a particular method

String.respond_to?(:prepend)
true
String.respond_to?(:append)
false

Modules

Modules are used for combining similar methods, so that other classes or modules can use it. You can not instantiate a module (like abstract classes in Java)

module MyRandomHelper
    def roll_dice
      rand(1..6)
    end
end

class Person
    attr_accessor :name, :number
end

class Player < Person
    include MyRandomHelper
    attr_accessor :score
end

p = Player.new
p.roll_dice

TODO

Operator Overloading

class Vector
    attr_accessor :x, :y

     def initialize(x, y)
        @x = x
        @y = y
    end

    def +(second)
        Vector.new(@x + second.x, @y + second.y)
    end

    def -(second)
        Vector.new(@x - second.x, @y - second.y)
    end

    def *(second)
        Vector.new(@x * second.x, @y * second.y)
    end

    def /(second)
        Vector.new(@x / second.x, @y / second.y)
    end

    def to_s
        return "(#{@x}, #{@y})"
    end

end

v1 = Vector.new(5, 10)
v2 = Vector.new(4, 9)

puts v1 + v2
puts v1 - v2
puts v1 * v2
puts v1 / v2

Exception Handling

begin
    puts 'before the raise'
    raise 'raise an exception'
    puts 'after the raise'
rescue
    puts 'rescued'
end

begin
    raise StandardError, 'standard error occurred'
rescue StandardError => e
    puts "#{e.class}: #{e.message}"
    puts e.backtrace.inspect
end

$! contains the raised exception $@ contains the exception backtrace

begin
    raise StandardError, 'standard error occurred'
rescue StandardError
    puts "#{$!.class}: #{$!.message}"
    puts "#{$@}"
end

retry re-executes the code inside begin end block

retry_count = 1

begin
    puts "retry count: #{retry_count}"
    retry_count += 1
    raise 'raise an exception'
rescue
    retry if retry_count <= 5
end

Custom exception

class MyException < Exception
end

begin
    raise MyException, 'my exception occurred'
rescue MyException
    puts "#{$!.class}: #{$!.message}"
    puts "#{$@}"
end

Catch multiple exceptions

begin
    raise 'i am a string'.call
rescue NoMethodError => e
    puts "#{$!.class}: #{$!.message}"
rescue ZeroDivisionError => e
    puts "#{$!.class}: #{$!.message}"
end

Further readings

Regular expression

a = "Better a diamond with a flaw than a pebble without"
a[/(\w+)/]

# output
# "Better"

a[/(\w+) (\w+)/]

# output
# "Better a"

a[/(?<one>\w+) (?<two>\w+)/, :two]
# output
# "a"

Miscellaneous

How to generate random number

rand(max=0)

# when calling it without an argument, rand returns a floating point number between 0.0 (including) and 1.0 (excluding), under the hood max.to_i.abs == 0
rand

# output
# 0.055758056734957595

# when the argument value is greater than or equal to 1, rand returns a integer between 0 (including) and that number (excluding), under the hood max.to_i.abs >= 1
rand(100)

# output
# 7

# generating number between 2 numbers both inclusive
rand(150..170)

# output
# 167

# generating number between 2 numbers, the last number is not inclusive
rand(1...10)

# output
# 4

Check the syntax of a Ruby file

ruby -c filename.rb

Concatenate String in a loop

words = ["Lorem", "ipsum", "dolor", "sit", "amet"]
words.map { |word| word.downcase }.join(' ')

# output
# "lorem ipsum dolor sit amet"

CamelCase String split

sentence = "ThereIsNoSpoon"
words = sentence.split(/(?=[A-Z])/)

# output
# ["There", "Is", "No", "Spoon"]

Ruby scripts

<a href="https://github.com/lifeparticle/Ruby-Cheatsheet/tree/master/Scripts"><img alt="ruby-scripts" src="https://img.shields.io/badge/ruby-scripts-red.svg?style=flat"/></a>

Platforms that supports Ruby

1. Heroku
2. Vercel
3. AWS Lambda
4. Fly.io

Ruby frameworks

1. Ruby on Rails
2. Sinatra
3. Padrino
4. Camping
5. Goliath
6. Hanami
7. NYNY
8. Cuba
9. Grape
10. Scorched
11. Roda
12. Volt
13. Hobbit
14. Cramp

My Ruby Articles

1. A Beginner’s Guide To Ruby
2. 17 Useful Ruby String Methods to Clean and Format Your Data
3. How to Deploy a Ruby Serverless Function to Vercel
4. Useful Ruby Array Methods to Manage Your Data
5. An Introduction to Ruby Hashes
6. How to Dockerize an Existing Sinatra Application
7. How To Dockerize an Existing Ruby on Rails Application
8. How To Parse Data Using Ruby and Selenium

Books and other resources

1. Ruby doc
2. How to use Ruby’s English and/or operators without going nuts
3. What is attr_accessor in Ruby?
4. Ruby Module Mixin Awesomeness
5. Tutorials
6. Pattern matching - New feature in Ruby 2.7
7. Awesome Ruby Blogs
8. Ruby Scripts
9. Awesome Ruby
10. Ruby Bookmarks
11. Code With Jason

Bug Reports and Feature Requests

Please create an issue with as much information you can. Thank you.

Contribution Guidelines

<a href="https://github.com/lifeparticle/Ruby-Cheatsheet/blob/master/CONTRIBUTING.md"><img alt="contribution guidelines" src="https://img.shields.io/badge/contribution-guidelines-brightgreen.svg?style=flat"/></a>

Author

Mahbub Zaman (https://mahbub.ninja)

License

MIT License