185 lines
3.7 KiB
Markdown
185 lines
3.7 KiB
Markdown
<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# Pluck
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> Extract a property value from each element of an object array.
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<section class="intro">
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var pluck = require( '@stdlib/utils/pluck' );
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```
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#### pluck( arr, prop\[, options] )
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Extracts a property value from each element of an object `array`.
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<!-- eslint-disable object-curly-newline, object-property-newline -->
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```javascript
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var arr = [
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{ 'a': 1, 'b': 2 },
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{ 'a': 0.5, 'b': 3 }
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];
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var out = pluck( arr, 'a' );
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// returns [ 1, 0.5 ]
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```
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The function accepts the following `options`:
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- **copy**: `boolean` indicating whether to return a new data structure. Default: `true`.
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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`.
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<!-- eslint-disable object-curly-newline, object-property-newline -->
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```javascript
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var arr = [
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{ 'a': 1, 'b': 2 },
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{ 'a': 0.5, 'b': 3 }
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];
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var out = pluck( arr, 'a', { 'copy': false } );
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// returns [ 1, 0.5 ]
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var bool = ( arr[ 0 ] === out[ 0 ] );
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// returns true
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- The function skips `null` and `undefined` array elements.
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<!-- eslint-disable object-curly-newline, object-property-newline -->
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```javascript
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var arr = [
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{ 'a': 1, 'b': 2 },
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null,
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void 0,
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{ 'a': 0.5, 'b': 3 }
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];
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var out = pluck( arr, 'a' );
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// returns [ 1, , , 0.5 ]
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```
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- Extracted values are **not** cloned.
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<!-- eslint-disable object-curly-newline, object-curly-spacing -->
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```javascript
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var arr = [
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{ 'a': { 'b': 2 } },
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{ 'a': { 'b': 3 } }
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];
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var out = pluck( arr, 'a' );
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// returns [ { 'b': 2 }, { 'b': 3 } ]
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var bool = ( arr[ 0 ].a === out[ 0 ] );
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// returns true
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```
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To prevent unintended mutation, use [copy][@stdlib/utils/copy].
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<!-- eslint-disable object-curly-newline, object-curly-spacing -->
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```javascript
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var copy = require( '@stdlib/utils/copy' );
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var arr = [
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{ 'a': { 'b': 2 } },
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{ 'a': { 'b': 3 } }
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];
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var out = pluck( arr, 'a' );
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// returns [ { 'b': 2 }, { 'b': 3 } ]
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// Perform a deep copy:
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out = copy( out );
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var bool = ( arr[ 0 ].a === out[ 0 ] );
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// returns false
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```
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var randu = require( '@stdlib/random/base/randu' );
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var round = require( '@stdlib/math/base/special/round' );
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var pluck = require( '@stdlib/utils/pluck' );
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var arr;
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var tmp;
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var out;
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var i;
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var j;
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// Generate a 100x5 2d-array...
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arr = new Array( 100 );
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for ( i = 0; i < arr.length; i++ ) {
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tmp = new Array( 5 );
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for ( j = 0; j < tmp.length; j++ ) {
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tmp[ j ] = round( randu()*100.0*(j+1.0) );
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}
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arr[ i ] = tmp;
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}
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// Pluck the 3rd column:
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out = pluck( arr, 2 );
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console.log( out );
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[@stdlib/utils/copy]: https://www.npmjs.com/package/@stdlib/utils/tree/main/copy
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</section>
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<!-- /.links -->
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