Deep Pluck

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

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