210 lines
4.8 KiB
Markdown
210 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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# everyBy
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> Test whether all elements in a collection pass a test implemented by a predicate function.
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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 everyBy = require( '@stdlib/utils/every-by' );
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```
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#### everyBy( collection, predicate\[, thisArg ] )
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Tests whether all elements in a `collection` pass a test implemented by a `predicate` function.
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```javascript
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function isPositive( value ) {
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return ( value > 0 );
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}
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var arr = [ 1, 2, 3, 4 ];
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var bool = everyBy( arr, isPositive );
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// returns true
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```
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If a `predicate` function returns a non-truthy value, the function **immediately** returns `false`.
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```javascript
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function isPositive( value ) {
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return ( value > 0 );
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}
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var arr = [ 1, -2, 3, 4 ];
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var bool = everyBy( arr, isPositive );
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// returns false
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```
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The invoked `function` is provided three arguments:
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- `value`: collection element
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- `index`: collection index
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- `collection`: input collection
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To set the function execution context, provide a `thisArg`.
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```javascript
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function sum( value ) {
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if ( value < 0 ) {
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return false;
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}
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this.sum += value;
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this.count += 1;
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return true;
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}
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var arr = [ 1, 2, 3, 4 ];
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var context = {
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'sum': 0,
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'count': 0
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};
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var bool = everyBy( arr, sum, context );
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// returns true
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var mean = context.sum / context.count;
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// returns 2.5
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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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- 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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- If provided an empty collection, the function returns `true`.
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```javascript
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function untrue() {
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return false;
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}
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var bool = everyBy( [], untrue );
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// returns true
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```
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- The function differs from [`Array.prototype.every`][mdn-array-every] in the following ways:
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- The function does **not** skip `undefined` elements.
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<!-- eslint-disable no-sparse-arrays, stdlib/doctest-marker -->
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```javascript
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function log( value, index ) {
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console.log( '%s: %s', index, value );
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return true;
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}
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var arr = [ 1, , , 4 ];
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var bool = everyBy( arr, log );
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/* =>
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0: 1
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1: undefined
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2: undefined
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3: 4
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*/
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```
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- The function provides limited support for dynamic collections (i.e., collections whose `length` changes during execution).
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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 everyBy = require( '@stdlib/utils/every-by' );
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function isPositive( value ) {
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return ( value > 0 );
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}
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var bool;
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var arr;
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var i;
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arr = new Array( 100 );
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for ( i = 0; i < arr.length; i++ ) {
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arr[ i ] = randu();
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}
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bool = everyBy( arr, isPositive );
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// returns <boolean>
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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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[mdn-array-every]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every
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</section>
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<!-- /.links -->
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