# Pluck
> Extract a property value from each element of an object array.
## Usage
```javascript
var pluck = require( '@stdlib/utils/pluck' );
```
#### pluck( arr, prop\[, options] )
Extracts a property value from each element of an object `array`.
```javascript
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`.
```javascript
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.
```javascript
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.
```javascript
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][@stdlib/utils/copy].
```javascript
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
```javascript
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 );
```
[@stdlib/utils/copy]: https://www.npmjs.com/package/@stdlib/utils/tree/main/copy