@stdlib/utils-deep-pluck NPM

Deep Pluck

Extract a nested property value from each element of an object array.

Installation

npm install @stdlib/utils-deep-pluck

Usage

var deepPluck = require( '@stdlib/utils-deep-pluck' );

deepPluck( arr, path[, options] )

Extracts a nested property value from each element of an object array based on a key path.

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

var out = deepPluck( arr, 'a.b.c' );
// returns [ 1, 2 ]

A key path may be specified as either a string or as an array.

var arr = [
    { 'a': [ 0, 1, 2 ] },
    { 'a': [ 3, 4, 5 ] }
];

var out = deepPluck( arr, [ 'a', 1 ] );
// returns [ 1, 4 ]

The function accepts the following options:

copy: boolean indicating whether to return a new data structure. Default: true.
sep: key path separator. Default: '.'.

By default, the function returns a new data structure. To mutate the input data structure (e.g., when input values can be discarded or when optimizing memory usage), set the copy option to false.

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

var out = deepPluck( arr, 'a.b.c', { 'copy': false } );
// returns [ 1, 2 ]

var bool = ( arr[ 0 ] === out[ 0 ] );
// returns true

The default key path separator is .. To specify an alternative separator, set the sep option.

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

var out = deepPluck( arr, 'a|b|c', { 'sep': '|' } );
// returns [ 1, 2 ]

If a key path does not exist, the function sets the plucked value as undefined.

var arr = [
    { 'a': { 'b': { 'c': 1 } } },
    null,
    void 0,
    { 'a': { 'b': { 'c': 2 } } }
];

var out = deepPluck( arr, 'a.b.c' );
// returns [ 1, undefined, undefined, 2 ]

Extracted values are not cloned.

var arr = [
    { 'a': { 'b': { 'c': 2 } } },
    { 'a': { 'b': { 'c': 3 } } }
];

var out = deepPluck( arr, 'a.b' );
// returns [ { 'c': 2 }, { 'c': 3 } ]

var bool = ( arr[ 0 ].a.b === out[ 0 ] );
// returns true

To prevent subsequent unintended mutation, use copy.

var copy = require( '@stdlib/utils-copy' );

var arr = [
    { 'a': { 'b': { 'c': 2 } } },
    { 'a': { 'b': { 'c': 3 } } }
];

var out = deepPluck( arr, 'a.b' );
// returns [ { 'c': 2 }, { 'c': 3 } ]

// Perform a deep copy:
out = copy( out );

var bool = ( arr[ 0 ].a.b === out[ 0 ] );
// returns false

Examples

var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var deepPluck = require( '@stdlib/utils-deep-pluck' );

var arr;
var out;
var tmp;
var i;

arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
    tmp = {
        'a': {
            'b': {
                'c': {
                    'd': null
                }
            }
        }
    };
    tmp.a.b.c.d = round( randu()*100.0 );
    arr[ i ] = tmp;
}

// Pluck the deeply nested values:
out = deepPluck( arr, 'a.b.c.d' );
console.log( out );

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.