stdlib-js / utils-object-inverse

Invert an object, such that keys become values and values become keys.

About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

Object Inverse

Invert an object, such that keys become values and values become keys.

Installation

npm install @stdlib/utils-object-inverse

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md 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

var invert = require( '@stdlib/utils-object-inverse' );

invert( obj[, options] )

Inverts an object, such that keys become values and values become keys.

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.

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.

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' }

Notes

• Beware when providing objects having values which are themselves objects. This implementation relies on native object serialization (#toString) when converting values to keys.

  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. In practice, however, most engines use insertion order to sort an object's keys, thus allowing for deterministic inversion.

Examples

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 );

---

See Also

• @stdlib/utils-object-inverse-by: invert an object, such that keys become values and values become keys, according to a transform function.

---

Notice

This package is part of 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, see the main project repository.

Community

---

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.