Awesome

jaro_winkler is an implementation of Jaro-Winkler similarity algorithm which is written in C extension and will fallback to pure Ruby version in platforms other than MRI/KRI like JRuby or Rubinius. Both of C and Ruby implementation support any kind of string encoding, such as UTF-8, EUC-JP, Big5, etc.

Installation

gem install jaro_winkler

Usage

require 'jaro_winkler'

# Jaro Winkler Similarity

JaroWinkler.similarity "MARTHA", "MARHTA"
# => 0.9611
JaroWinkler.similarity "MARTHA", "marhta", ignore_case: true
# => 0.9611
JaroWinkler.similarity "MARTHA", "MARHTA", weight: 0.2
# => 0.9778

# Jaro Similarity

JaroWinkler.jaro_similarity "MARTHA", "MARHTA"
# => 0.9444444444444445

There is no JaroWinkler.jaro_winkler_similarity, it's tediously long.

Options

Name	Type	Default	Note
ignore_case	boolean	false	All lower case characters are converted to upper case prior to the comparison.
weight	number	0.1	A constant scaling factor for how much the score is adjusted upwards for having common prefixes.
threshold	number	0.7	The prefix bonus is only added when the compared strings have a Jaro similarity above the threshold.
adj_table	boolean	false	The option is used to give partial credit for characters that may be errors due to known phonetic or character recognition errors. A typical example is to match the letter "O" with the number "0".

Adjusting Table

Default Table

['A', 'E'], ['A', 'I'], ['A', 'O'], ['A', 'U'], ['B', 'V'], ['E', 'I'], ['E', 'O'], ['E', 'U'], ['I', 'O'], ['I', 'U'],
['O', 'U'], ['I', 'Y'], ['E', 'Y'], ['C', 'G'], ['E', 'F'], ['W', 'U'], ['W', 'V'], ['X', 'K'], ['S', 'Z'], ['X', 'S'],
['Q', 'C'], ['U', 'V'], ['M', 'N'], ['L', 'I'], ['Q', 'O'], ['P', 'R'], ['I', 'J'], ['2', 'Z'], ['5', 'S'], ['8', 'B'],
['1', 'I'], ['1', 'L'], ['0', 'O'], ['0', 'Q'], ['C', 'K'], ['G', 'J'], ['E', ' '], ['Y', ' '], ['S', ' ']

How it works?

Original Formula:

$\begin{cases}0&{\text{if }m=0}\\\frac{1}{3}(\frac{m}{\left|s1\right|}+\frac{m}{\left|s2\right|}+\frac{m-t}{m})&\text{others}\end{cases}$

where

m is the number of matching characters.
t is half the number of transpositions.

With Adjusting Table:

$\begin{cases}0&\text{if }m=0\\\frac{1}{3}(\frac{\frac{s}{10}+m}{\left|s1\right|}+\frac{\frac{s}{10}+m}{\left|s2\right|}+\frac{m-t}{m})&\text{others}\end{cases}$

where

s is the number of nonmatching but similar characters.

Why This?

There is also another similar gem named fuzzy-string-match which both provides C and Ruby version as well.

I reinvent this wheel because of the naming in fuzzy-string-match such as getDistance breaks convention, and some weird code like a1 = s1.split( // ) (s1.chars could be better), furthermore, it's bugged (see tables below).

Compare with other gems

	jaro_winkler	fuzzystringmatch	hotwater	amatch
Encoding Support	Yes	Pure Ruby only	No	No
Windows Support	Yes	?	No	Yes
Adjusting Table	Yes	No	No	No
Native	Yes	Yes	Yes	Yes
Pure Ruby	Yes	Yes	No	No
Speed	1st	3rd	2nd	4th

I made a table below to compare accuracy between each gem:

str_1	str_2	origin	jaro_winkler	fuzzystringmatch	hotwater	amatch
"henka"	"henkan"	0.9667	0.9667	0.9722	0.9667	0.9444
"al"	"al"	1.0	1.0	1.0	1.0	1.0
"martha"	"marhta"	0.9611	0.9611	0.9611	0.9611	0.9444
"jones"	"johnson"	0.8324	0.8324	0.8324	0.8324	0.7905
"abcvwxyz"	"cabvwxyz"	0.9583	0.9583	0.9583	0.9583	0.9583
"dwayne"	"duane"	0.84	0.84	0.84	0.84	0.8222
"dixon"	"dicksonx"	0.8133	0.8133	0.8133	0.8133	0.7667
"fvie"	"ten"	0.0	0.0	0.0	0.0	0.0

The "origin" result is from the original C implementation by the author of the algorithm.
Test data are borrowed from fuzzy-string-match's rspec file.

Benchmark

$ bundle exec rake benchmark
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-darwin16]

# C Extension
Rehearsal --------------------------------------------------------------
jaro_winkler (8c16e09)       0.240000   0.000000   0.240000 (  0.241347)
fuzzy-string-match (1.0.1)   0.400000   0.010000   0.410000 (  0.403673)
hotwater (0.1.2)             0.250000   0.000000   0.250000 (  0.254503)
amatch (0.4.0)               0.870000   0.000000   0.870000 (  0.875930)
----------------------------------------------------- total: 1.770000sec

                                 user     system      total        real
jaro_winkler (8c16e09)       0.230000   0.000000   0.230000 (  0.236921)
fuzzy-string-match (1.0.1)   0.380000   0.000000   0.380000 (  0.381942)
hotwater (0.1.2)             0.250000   0.000000   0.250000 (  0.254977)
amatch (0.4.0)               0.860000   0.000000   0.860000 (  0.861207)

# Pure Ruby
Rehearsal --------------------------------------------------------------
jaro_winkler (8c16e09)       0.440000   0.000000   0.440000 (  0.438470)
fuzzy-string-match (1.0.1)   0.860000   0.000000   0.860000 (  0.862850)
----------------------------------------------------- total: 1.300000sec

                                 user     system      total        real
jaro_winkler (8c16e09)       0.440000   0.000000   0.440000 (  0.439237)
fuzzy-string-match (1.0.1)   0.910000   0.010000   0.920000 (  0.920259)

Todo

Custom adjusting word table.