mapeo-entity-filter

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.

$3

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

$3

``javascript
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);
`

$3

#### 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.

`json
["==", "class", "street_major"]
`

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

`json
["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.

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