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Add iterator utility to step according to a provided callback function
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‎lib/node_modules/@stdlib/iter/strided-by/README.md‎

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<!--
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@license Apache-2.0
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Copyright (c) 2019 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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# iterStridedBy
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> Create an [iterator][mdn-iterator-protocol] which steps according to a provided callback 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 iterStridedBy = require( '@stdlib/iter/strided-by' );
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```
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#### iterStridedBy( iterator, fcn\[, offset\[, eager]]\[, thisArg] )
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Returns an [iterator][mdn-iterator-protocol] which steps according to a provided callback function.
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```javascript
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var array2iterator = require( '@stdlib/array/to-iterator' );
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function stride( v, i ) {
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return (i % 10) + 1;
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}
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var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
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var it = iterStridedBy( arr, stride );
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// returns <Object>
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var r = it.next().value;
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// returns 1
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r = it.next().value;
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// returns 2
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r = it.next().value;
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// returns 4
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// ...
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```
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The returned [iterator][mdn-iterator-protocol] protocol-compliant object has the following properties:
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- **next**: function which returns an [iterator][mdn-iterator-protocol] protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the iterator is finished.
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- **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an [iterator][mdn-iterator-protocol] protocol-compliant object.
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The callback function is provided four arguments:
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- **value**: iterated value
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- **i**: source iteration index (zero-based)
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- **n**: iteration index (zero-based)
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- **curr**: current stride
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To set the callback execution context, provide a `thisArg`.
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<!-- eslint-disable no-invalid-this -->
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```javascript
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var array2iterator = require( '@stdlib/array/to-iterator' );
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function stride( v, i ) {
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this.count += 1;
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return (i % 10) + 1;
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}
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var ctx = {
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'count': 0
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};
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var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
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var it = iterStridedBy( arr, stride, ctx );
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// returns <Object>
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var v = it.next().value;
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// returns 1
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v = it.next().value;
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// returns 2
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v = it.next().value;
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// returns 4
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v = it.next().value;
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// returns 8
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var count = ctx.count;
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// returns 4
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```
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To skip the first `N` values of a provided [`iterator`][mdn-iterator-protocol], provide an `offset` argument.
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```javascript
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var array2iterator = require( '@stdlib/array/to-iterator' );
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function stride( v, i ) {
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return (i % 10) + 1;
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}
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var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
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var it = iterStridedBy( arr, stride, 1 );
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// returns <Object>
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var r = it.next().value;
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// returns 2
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r = it.next().value;
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// returns 4
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r = it.next().value;
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// returns 8
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// ...
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```
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By default, the returned [iterator][mdn-iterator-protocol] defers consuming the first `N` input [`iterator`][mdn-iterator-protocol] values until the first value of the returned [iterator][mdn-iterator-protocol] is consumed. To eagerly advance the input [`iterator`][mdn-iterator-protocol], set the `eager` argument to `true`.
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```javascript
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var array2iterator = require( '@stdlib/array/to-iterator' );
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function stride() {
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return 1;
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}
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var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
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var it = iterStridedBy( arr, stride, 4, true );
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// returns <Object>
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var r = it.next().value;
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// returns 5
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r = it.next().value;
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// returns 6
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r = it.next().value;
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// returns 7
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// ...
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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 callback function **must** return a **positive integer** value.
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- If an environment supports `Symbol.iterator` **and** a provided [iterator][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.
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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/iter/randu' );
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var discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory;
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var iterStridedBy = require( '@stdlib/iter/strided-by' );
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// Create a seeded iterator for generating pseudorandom numbers:
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var rand = randu({
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'seed': 1234,
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'iter': 10
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});
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// Create a PRNG for generating pseudorandom integers on the interval [1,10]:
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var randi = discreteUniform( 1, 10, {
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'seed': 4321
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});
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// Create an iterator which randomly selects input iterator values:
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var it = iterStridedBy( rand, randi );
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// Perform manual iteration...
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var r;
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while ( true ) {
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r = it.next();
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if ( r.done ) {
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break;
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}
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console.log( r.value );
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}
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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-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/iter/strided-by/benchmark/benchmark.js‎

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2019 The Stdlib Authors.
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*
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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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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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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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'use strict';
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// MODULES //
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var bench = require( '@stdlib/bench' );
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var randu = require( '@stdlib/random/iter/randu' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var isIteratorLike = require( '@stdlib/assert/is-iterator-like' );
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var pkg = require( './../package.json' ).name;
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var iterStridedBy = require( './../lib' );
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// MAIN //
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bench( pkg, function benchmark( b ) {
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var rand;
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var iter;
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var i;
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rand = randu();
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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iter = iterStridedBy( rand, stride );
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if ( typeof iter !== 'object' ) {
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b.fail( 'should return an object' );
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}
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}
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b.toc();
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if ( !isIteratorLike( iter ) ) {
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b.fail( 'should return an iterator protocol-compliant object' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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function stride( v, i ) {
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return (i % 10) + 1;
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}
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});
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bench( pkg+'::iteration', function benchmark( b ) {
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var rand;
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var iter;
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var z;
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var i;
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rand = randu();
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iter = iterStridedBy( rand, stride );
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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z = iter.next().value;
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if ( isnan( z ) ) {
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b.fail( 'should not return NaN' );
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}
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}
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b.toc();
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if ( isnan( z ) ) {
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b.fail( 'should not return NaN' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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function stride( v, i ) {
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return (i % 10) + 1;
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}
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});

‎lib/node_modules/@stdlib/iter/strided-by/docs/repl.txt‎

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{{alias}}( iterator, fcn[, offset[, eager]][, thisArg] )
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Returns an iterator which steps according to a provided callback function.
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When invoked, the input function is provided four arguments:
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- value: iterated value
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- i: input iteration index (zero-based)
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- n: output (strided) iteration index (zero-based)
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- curr: current stride
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The return value of the input function specifies the next stride.
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If an environment supports Symbol.iterator and a provided iterator is
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iterable, the returned iterator is iterable.
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Parameters
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----------
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iterator: Object
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Input iterator.
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fcn: Function
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Stride function (i.e., a function which returns the step amount).
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offset: integer (optional)
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Index of the first iterated value. Default: 0.
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eager: boolean (optional)
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Boolean indicating whether to eagerly advance the input iterator when
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provided a non-zero offset. Default: false.
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thisArg: any (optional)
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Stride function execution context.
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Returns
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-------
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iterator: Object
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Iterator.
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iterator.next(): Function
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Returns an iterator protocol-compliant object containing the next
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iterated value (if one exists) and a boolean flag indicating whether the
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iterator is finished.
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iterator.return( [value] ): Function
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Finishes an iterator and returns a provided value.
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Examples
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--------
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> var arr = {{alias:@stdlib/array/to-iterator}}( [ 0, 1, 2, 3, 4, 5, 6 ] );
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> function stride( v, i ) { return (i % 10)+1; };
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> var it = {{alias}}( arr, stride );
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> var r = it.next().value
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0
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> r = it.next().value
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1
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> r = it.next().value
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3
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See Also
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--------
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