Pluck

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

Installation

$ npm install utils-pluck

Usage

var pluck = require( 'utils-pluck' );

pluck( arr, prop[, opts] )

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 utils-copy.

  var copy = require( '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 round = require( 'math-round' );
var pluck = require( 'utils-pluck' );

var arr = new Array( 100 );
var tmp;
var i;
var j;

// Generate a 100x5 2d-array...
for ( i = 0; i < arr.length; i++ ) {
	tmp = new Array( 5 );
	for ( j = 0; j < tmp.length; j++ ) {
		tmp[ j ] = round( Math.random()*100*(j+1) );
	}
	arr[ i ] = tmp;
}

// Pluck the 3rd column:
var out = pluck( arr, 2 );

console.log( out );

To run the example code from the top-level application directory,

$ node ./examples/index.js

Tests

Unit

This repository uses tape for unit tests. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

Browser Support

This repository uses Testling for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:

$ make test-browsers

To view the tests in a local web browser,

$ make view-browser-tests

License

MIT license.

Copyright

Copyright © 2016. Athan Reines.