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Pluck

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

Installation

npm install @stdlib/utils-pluck

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

pluck( arr, prop[, options] )

Extracts a property value from each element of an object array.

var arr = [
    { 'a': 1, 'b': 2 },
    { 'a': 0.5, 'b': 3 }
];

var out = pluck( arr, 'a' );
// returns [ 1, 0.5 ]

The function accepts the following options:

• copy: boolean indicating whether to return a new data structure. Default: true.

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': 1, 'b': 2 },
    { 'a': 0.5, 'b': 3 }
];

var out = pluck( arr, 'a', { 'copy': false } );
// returns [ 1, 0.5 ]

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

Notes

• The function skips null and undefined array elements.

  var arr = [
      { 'a': 1, 'b': 2 },
      null,
      void 0,
      { 'a': 0.5, 'b': 3 }
  ];
  
  var out = pluck( arr, 'a' );
  // returns [ 1, , , 0.5 ]

• Extracted values are not cloned.

  var arr = [
      { 'a': { 'b': 2 } },
      { 'a': { 'b': 3 } }
  ];
  
  var out = pluck( arr, 'a' );
  // returns [ { 'b': 2 }, { 'b': 3 } ]
  
  var bool = ( arr[ 0 ].a === out[ 0 ] );
  // returns true

  To prevent unintended mutation, use copy.

  var copy = require( '@stdlib/utils-copy' );
  
  var arr = [
      { 'a': { 'b': 2 } },
      { 'a': { 'b': 3 } }
  ];
  
  var out = pluck( arr, 'a' );
  // returns [ { 'b': 2 }, { 'b': 3 } ]
  
  // Perform a deep copy:
  out = copy( out );
  
  var bool = ( arr[ 0 ].a === out[ 0 ] );
  // returns false

Examples

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

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

// Generate a 100x5 2d-array...
arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
    tmp = new Array( 5 );
    for ( j = 0; j < tmp.length; j++ ) {
        tmp[ j ] = round( randu()*100.0*(j+1.0) );
    }
    arr[ i ] = tmp;
}
// Pluck the 3rd column:
out = pluck( arr, 2 );
console.log( out );

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See Also

• @stdlib/utils-deep-pluck: extract a nested property value from each element of an object array.
• @stdlib/utils-pick: return a partial object copy containing only specified keys.

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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.