Invert an object, such that keys become values and values become keys.
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> Invert an object, such that keys become values and values become keys.
``bash`
npm install @stdlib/object-inverse
`javascript`
var invert = require( '@stdlib/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.
`javascripta
var obj = {};
obj.a = 'beep';
obj.b = 'boop';
obj.c = 'beep'; // inserted after
var out = invert( obj, {
'duplicates': false
});
// returns { 'beep': 'c', 'boop': 'b' }
`
- Beware when providing 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 discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var objectKeys = require( '@stdlib/utils-keys' );
var invert = require( '@stdlib/object-inverse' );
// Create an array of random integers:
var arr = discreteUniform( 1000, 0, 100 );
// Invert the array to determine value frequency:
var out = invert( arr );
var keys = objectKeys( out );
// Compute the frequencies...
var i;
for ( i = 0; i < keys.length; i++ ) {
if ( out[ i ] ) {
out[ i ] = out[ i ].length;
} else {
out[ i ] = 0;
}
}
console.dir( out );
`
*
- [@stdlib/object-inverse-by][@stdlib/object/inverse-by]: invert an object, such that keys become values and values become keys, according to a transform function.
*
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
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---
See [LICENSE][stdlib-license].
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
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[umd]: https://github.com/umdjs/umd
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[deno-url]: https://github.com/stdlib-js/object-inverse/tree/deno
[deno-readme]: https://github.com/stdlib-js/object-inverse/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/object-inverse/tree/umd
[umd-readme]: https://github.com/stdlib-js/object-inverse/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/object-inverse/tree/esm
[esm-readme]: https://github.com/stdlib-js/object-inverse/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/object-inverse/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/object-inverse/main/LICENSE
[ecma-262-for-in]: https://262.ecma-international.org/5.1/#sec-12.6.4
[@stdlib/object/inverse-by]: https://www.npmjs.com/package/@stdlib/object-inverse-by