README.md

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keyByRight

Convert a collection to an object whose keys are determined by a provided function and whose values are the collection values, iterating from right to left.

Installation

npm install @stdlib/utils-key-by-right

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 keyByRight = require( '@stdlib/utils-key-by-right' );

keyByRight( collection, fcn[, thisArg ] )

Converts a collection to an object whose keys are determined by a provided function and whose values are the collection values, iterating from right to left.

function toKey( value ) {
    return value.a;
}

var arr = [
    { 'a': 1 },
    { 'a': 2 }
];

var out = keyByRight( arr, toKey );
// returns { '2': { 'a': 2 }, '1': { 'a': 1 } }

The invoked function is provided two arguments:

• value: collection element.
• index: collection index.

To set the function execution context, provide a thisArg.

function toKey( value, index ) {
    this.sum += value;
    this.count += 1;
    return index;
}

var arr = [ 1, 2, 3, 4 ];

var context = {
    'sum': 0,
    'count': 0
};

var out = keyByRight( arr, toKey, context );
// returns { '3': 4, '2': 3, '1': 2, '0': 1 }

var mean = context.sum / context.count;
// returns 2.5

Notes

• A collection may be either an Array, Typed Array, or an array-like Object (excluding strings and functions).
• If more than one element in a collection resolves to the same key, the key value is the collection element which last resolved to the key.
• Object values are shallow copies.

Examples

var keyByRight = require( '@stdlib/utils-key-by-right' );

var arr;
var obj;
var i;

function toKey( value ) {
    return value.name;
}

arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
    arr[ i ] = {
        'name': 'v'+i,
        'value': i
    };
}

obj = keyByRight( arr, toKey );
console.log( obj );

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See Also

• @stdlib/utils-for-each-right: invoke a function for each element in a collection, iterating from right to left.
• @stdlib/utils-key-by: convert a collection to an object whose keys are determined by a provided function and whose values are the collection values.

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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

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.