stdlib-js
<summary>
About stdlib...
</summary>
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Object Inverse
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
Invert an object, such that keys become values and values become keys.
bash
npm install @stdlib/utils-object-inverse
javascript
var invert = require( '@stdlib/utils-object-inverse' );
#### invert( obj[, options] )
Inverts an object, such that keys become values and values become keys.
javascript
var out = invert({
'a': 'beep',
'b': 'boop'
});
// returns { 'beep': 'a', 'boop': 'b' }
The function accepts the following options:
- duplicates: boolean indicating whether to store keys mapped to duplicate values in arrays. Default: true.
By default, keys mapped to duplicate values are stored in arrays.
javascript
var out = invert({
'a': 'beep',
'b': 'beep'
});
// returns { 'beep': [ 'a', 'b' ] }
To not allow duplicates, set the duplicates option to false. The output key-value pair will be the key most recently inserted into the input object.
javascript
var obj = {};
obj.a = 'beep';
obj.b = 'boop';
obj.c = 'beep'; // inserted after `a`
var out = invert( obj, {
'duplicates': false
});
// returns { 'beep': 'c', 'boop': 'b' }
objects having values which are themselves objects. This implementation relies on native object serialization (#toString) when converting values to keys.
javascript
var obj = {
'a': [ 1, 2, 3 ],
'b': {
'c': 'd'
}
};
var out = invert( obj );
// returns { '1,2,3': 'a', '[object Object]': 'b' }
- Insertion order is not guaranteed, as object key enumeration is not specified according to the [ECMAScript specification][ecma-262-for-in]. In practice, however, most engines use insertion order to sort an object's keys, thus allowing for deterministic inversion.
javascript
var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var invert = require( '@stdlib/utils-object-inverse' );
var keys;
var arr;
var out;
var i;
// Create an array of random integers...
arr = new Array( 1000 );
for ( i = 0; i < arr.length; i++ ) {
arr[ i ] = round( randu()*100.0 );
}
// Invert the array to determine value frequency...
out = invert( arr );
keys = Object.keys( out );
for ( i = 0; i < keys.length; i++ ) {
if ( out[ i ] ) {
out[ i ] = out[ i ].length;
} else {
out[ i ] = 0;
}
}
console.dir( out );
@stdlib/utils-object-inverse-by][@stdlib/utils/object-inverse-by]: invert an object, such that keys become values and values become keys, according to a transform function.
