178 lines
4.8 KiB
Markdown
178 lines
4.8 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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# group
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> Group values as arrays associated with distinct keys.
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
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<section class="intro">
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</section>
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<!-- /.intro -->
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<!-- Package usage documentation. -->
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<section class="usage">
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## Usage
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```javascript
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var group = require( '@stdlib/utils/group' );
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```
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#### group( collection, \[options,] groups )
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Groups values as arrays associated with distinct keys.
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```javascript
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var arr = [ 'beep', 'boop', 'foo', 'bar' ];
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var groups = [ 'b', 'b', 'f', 'b' ];
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var out = group( arr, groups );
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// returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }
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```
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The function accepts the following `options`:
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- `returns`: specifies the output format. If the option equals `'values'`, the function outputs element values. If the option equals `'indices'`, the function outputs element indices. If the option equals `'*'`, the function outputs both element indices and values. Default: `'values'`.
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By default, the function returns element values. To return element indices, set the `returns` option to `'indices'`.
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```javascript
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var arr = [ 'beep', 'boop', 'foo', 'bar' ];
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var groups = [ 'b', 'b', 'f', 'b' ];
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var opts = {
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'returns': 'indices'
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};
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var out = group( arr, opts, groups );
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// returns { 'b': [ 0, 1, 3 ], 'f': [ 2 ] }
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```
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To return index-element pairs, set the `returns` option to `'*'`.
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```javascript
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var arr = [ 'beep', 'boop', 'foo', 'bar' ];
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var groups = [ 'b', 'b', 'f', 'b' ];
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var opts = {
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'returns': '*'
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};
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var out = group( arr, opts, groups );
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// returns { 'b': [ [ 0, 'beep' ], [ 1, 'boop' ], [ 3, 'bar' ] ], 'f': [ [ 2, 'foo' ] ] }
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```
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</section>
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<!-- /.usage -->
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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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## Notes
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- Both `collection` and `groups` **must** be collections. A collection may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`).
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- Each value in `groups` should resolve to a value which can be serialized as an `object` key. As a counterexample,
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```javascript
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var arr = [ 'beep', 'boop', 'foo', 'bar' ];
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var groups = [ {}, {}, {}, {} ];
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var out = group( arr, groups );
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// returns { '[object Object]': [ 'beep', 'boop', 'foo', 'bar' ] }
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```
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while each "group" is unique, all collection elements resolve to the same group because each group identifier serializes to the same `string`.
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</section>
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<!-- /.notes -->
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<!-- Package usage examples. -->
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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 floor = require( '@stdlib/math/base/special/floor' );
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var group = require( '@stdlib/utils/group' );
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var vals;
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var arr;
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var out;
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var g;
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var i;
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var j;
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vals = [ 'beep', 'boop', 'foo', 'bar', 'woot', 'woot' ];
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// Generate a random collection...
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arr = new Array( 100 );
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for ( i = 0; i < arr.length; i++ ) {
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j = floor( randu()*vals.length );
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arr[ i ] = vals[ j ];
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}
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// Randomly assign collection values to groups...
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g = new Array( arr.length );
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for ( i = 0; i < arr.length; i++ ) {
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g[ i ] = floor( randu()*vals.length );
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}
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// Compute the groups:
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out = group( arr, g );
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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 to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="references">
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</section>
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<!-- /.references -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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[mdn-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object
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</section>
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<!-- /.links -->
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