Pluck

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

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,
      undefined,
      {'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/math/base/random/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 );