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Mapeo Entity Filter

This library is forked from mapbox/feature-filter, but adapted to work with entities in the mapeo-core database. This library implements the semantics specified by the Mapbox GL JS spec, but supports arrays as keys as well as strings, in order to filter against nested tags.

API

compile(filter)

Given a filter expressed as nested arrays, return a new function that evaluates whether a given feature passes its test.

Parameters

parameter	type	description
`filter`	Array	mapbox gl filter

Returns Function, filter-evaluating function

Usage

var compile = require('mapeo-entity-filter');

// will match a feature with class of street_limited,
// AND an admin_level less than or equal to 3,
// that's NOT a polygon.
var filter = [
    "all",
    ["==", "class", "street_limited"],
    ["<=", "admin_level", 3]
]

// testFilter will be a function that returns a boolean
var testFilter = compile(filter);

// Layer feature that you're testing. Must have type
// and properties keys.
var entity = {
  tags: {
    class: "street_limited"
    admin_level: 1
  }
};

// will return a boolean based on whether the feature matched the filter
return testFilter(entity);

Filter expression language

Existential Filters

["has", key] object[key] exists

["!has", key] object[key] does not exist

Comparison Filters

["==", key, value] equality: object[key] = value

["!=", key, value] inequality: object[key] ≠ value

[">", key, value] greater than: object[key] > value

[">=", key, value] greater than or equal: object[key] ≥ value

["<", key, value] less than: object[key] < value

["<=", key, value] less than or equal: object[key] ≤ value

Set Membership Filters

["in", key, v0, ..., vn] set inclusion: object[key] ∈ {v0, ..., vn}

["!in", key, v0, ..., vn] set exclusion: object[key] ∉ {v0, ..., vn}

Combining Filters

["all", f0, ..., fn] logical AND: f0 ∧ ... ∧ fn

["any", f0, ..., fn] logical OR: f0 ∨ ... ∨ fn

["none", f0, ..., fn] logical NOR: ¬f0 ∧ ... ∧ ¬fn

A key must be a string that identifies a entity tag, or one of the following special keys:

$type: the entity type. This key may be used with the "==","!=", "in", and "!in" operators. Possible values are "observation", "node", and "way".
$id: the entity identifier. This key may be used with the "==","!=", "in", and "!in" operators.
$created: the timestamp the entity was created (ISO string).
$modified: the timestamp the entity was modified (ISO string).

A value (and v0, ..., vn for set operators) must be a string, number, or boolean to compare the tag value against.

Set membership filters are a compact and efficient way to test whether a field matches any of multiple values.

The comparison and set membership filters implement strictly-typed comparisons; for example, all of the following evaluate to false: 0 < "1", 2 == "2", "true" in [true, false].

The "all", "any", and "none" filter operators are used to create compound filters. The values f0, ..., fn must be filter expressions themselves.

["==", "class", "street_major"]

This filter requires that the class tag of each feature is equal to either "street_major", "street_minor", or "street_limited".

["in", "class", "street_major", "street_minor", "street_limited"]

The combining filter "all" takes the three other filters that follow it and requires all of them to be true for a feature to be included: a feature must have a class equal to "street_limited", its admin_level must be greater than or equal to 3.

[
  "all",
  ["==", "class", "street_limited"],
  [">=", "admin_level", 3]
]