https://github.com/stdlib-js/utils-object-inverse-by
Invert an object, such that keys become values and values become keys, according to a transform function.
https://github.com/stdlib-js/utils-object-inverse-by
convert inverse inverseby invert invertby javascript keys node node-js nodejs obj object object-like stdlib transform util utilities utility utils values
Last synced: 10 months ago
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Invert an object, such that keys become values and values become keys, according to a transform function.
- Host: GitHub
- URL: https://github.com/stdlib-js/utils-object-inverse-by
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-14T16:45:16.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2025-03-17T00:47:17.000Z (11 months ago)
- Last Synced: 2025-03-24T04:29:05.506Z (11 months ago)
- Topics: convert, inverse, inverseby, invert, invertby, javascript, keys, node, node-js, nodejs, obj, object, object-like, stdlib, transform, util, utilities, utility, utils, values
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 1.21 MB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
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README
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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, according to a transform function.
## Installation
```bash
npm install @stdlib/utils-object-inverse-by
```
Alternatively,
- To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).
The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.
To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
## Usage
```javascript
var invertBy = require( '@stdlib/utils-object-inverse-by' );
```
#### invertBy( obj, \[options,] transform )
Inverts an `object`, such that keys become values and values become keys, according to a `transform` function.
```javascript
function transform( key, value ) {
return value;
}
var obj = {
'a': 'beep',
'b': 'boop'
};
var out = invertBy( obj, transform );
// 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
function transform( key, value ) {
return value;
}
var obj = {
'a': 'beep',
'b': 'beep'
};
var out = invertBy( obj, transform );
// 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
function transform( key, value ) {
return value;
}
var obj = {};
obj.a = 'beep';
obj.b = 'boop';
obj.c = 'beep'; // inserted after `a`
var opts = {
'duplicates': false
};
var out = invertBy( obj, opts, transform );
// returns { 'beep': 'c', 'boop': 'b' }
```
The `transform` function is provided three arguments:
- **key**: object key.
- **value**: object value corresponding to `key`.
- **obj**: input object.
```javascript
function transform( key, value, o ) {
if ( key === 'name' ) {
return value;
}
return o.name + ':' + value;
}
var obj = {
'name': 'foo',
'a': 'beep',
'b': 'boop'
};
var out = invertBy( obj, transform );
// returns { 'foo': 'name', 'foo:beep': 'a', 'foo:boop': 'b' }
```
## Notes
- Beware when providing `objects` having values which are themselves `objects`. This function relies on native `object` serialization (`#toString`) when converting `transform` function return values to keys.
```javascript
function transform( key, value ) {
return value;
}
var obj = {
'a': [ 1, 2, 3 ],
'b': {
'c': 'd'
}
};
var out = invertBy( obj, transform );
// 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.
## Examples
```javascript
var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var invertBy = require( '@stdlib/utils-object-inverse-by' );
var keys;
var arr;
var out;
var i;
function transform( key, value ) {
return value;
}
// 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 = invertBy( arr, transform );
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 );
```
* * *
## See Also
- [`@stdlib/utils-object-inverse`][@stdlib/utils/object-inverse]: invert an object, such that keys become values and values become keys.
* * *
## Notice
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].
#### Community
[![Chat][chat-image]][chat-url]
---
## License
See [LICENSE][stdlib-license].
## Copyright
Copyright © 2016-2025. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/utils-object-inverse-by.svg
[npm-url]: https://npmjs.org/package/@stdlib/utils-object-inverse-by
[test-image]: https://github.com/stdlib-js/utils-object-inverse-by/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/utils-object-inverse-by/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/utils-object-inverse-by/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/utils-object-inverse-by?branch=main
[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/utils-object-inverse-by/tree/deno
[deno-readme]: https://github.com/stdlib-js/utils-object-inverse-by/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/utils-object-inverse-by/tree/umd
[umd-readme]: https://github.com/stdlib-js/utils-object-inverse-by/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/utils-object-inverse-by/tree/esm
[esm-readme]: https://github.com/stdlib-js/utils-object-inverse-by/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/utils-object-inverse-by/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/utils-object-inverse-by/main/LICENSE
[ecma-262-for-in]: https://262.ecma-international.org/5.1/#sec-12.6.4
[@stdlib/utils/object-inverse]: https://github.com/stdlib-js/utils-object-inverse