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feat: add ndarray/iter/select-dimension 
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‎lib/node_modules/@stdlib/ndarray/iter/select-dimension/README.md

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<!--
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@license Apache-2.0
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Copyright (c) 2024 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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# nditerSelectDimension
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> Create an iterator which iterates over each view along a specified dimension.
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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 nditerSelectDimension = require( '@stdlib/ndarray/iter/select-dimension' );
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```
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#### nditerSelectDimension( x, dim\[, options] )
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Returns an iterator which iterates over each view along a specified dimension.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var x = array( [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 5, 6 ], [ 7, 8 ] ] ] );
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// returns <ndarray>
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var iter = nditerSelectDimension( x, 0 );
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var v = iter.next().value;
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// returns <ndarray>
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var arr = ndarray2array( v );
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// returns [ [ 1, 2 ], [ 3, 4 ] ]
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v = iter.next().value;
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// returns <ndarray>
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arr = ndarray2array( v );
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// returns [ [ 5, 6 ], [ 7, 8 ] ]
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// ...
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```
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The function accepts the following `options`:
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- **readonly**: boolean indicating whether returned [`ndarray`][@stdlib/ndarray/ctor] views should be read-only. In order to return writable [`ndarray`][@stdlib/ndarray/ctor] views, the input [`ndarray`][@stdlib/ndarray/ctor] must be writable. If the input [`ndarray`][@stdlib/ndarray/ctor] is read-only, setting this option to `false` raises an exception. Default: `true`.
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- **keepdim**: boolean indicating whether returned [`ndarray`][@stdlib/ndarray/ctor] views should include the selected dimension as a singleton dimension. If `true`, each returned view has the same number of dimensions as the input [`ndarray`][@stdlib/ndarray/ctor]. Otherwise, each returned view has one fewer dimensions than the input [`ndarray`][@stdlib/ndarray/ctor]. Default: `false`.
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By default, the iterator returns [`ndarray`][@stdlib/ndarray/ctor] views which are **read-only**. To return writable [views][@stdlib/ndarray/slice], set the `readonly` option to `false`.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var x = array( [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 5, 6 ], [ 7, 8 ] ] ] );
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// returns <ndarray>
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var iter = nditerSelectDimension( x, 0, {
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'readonly': false
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});
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var v = iter.next().value;
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// returns <ndarray>
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var arr = ndarray2array( v );
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// returns [ [ 1, 2 ], [ 3, 4 ] ]
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v.set( 0, 0, 10 );
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arr = ndarray2array( v );
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// returns [ [ 10, 2 ], [ 3, 4 ] ]
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```
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By default, the iterator returns [`ndarray`][@stdlib/ndarray/ctor] views which omit the selected dimension, resulting in [`ndarray`][@stdlib/ndarray/ctor] views having one fewer dimensions than the provided input [`ndarray`][@stdlib/ndarray/ctor]. To include the selected dimension as a singleton dimension in the returned [`ndarray`][@stdlib/ndarray/ctor] views, set the `keepdim` option to `true`.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var x = array( [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 5, 6 ], [ 7, 8 ] ] ] );
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// returns <ndarray>
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var iter = nditerSelectDimension( x, 0, {
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'keepdim': true
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});
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var v = iter.next().value;
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// returns <ndarray>
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var arr = ndarray2array( v );
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// returns [ [ [ 1, 2 ], [ 3, 4 ] ] ]
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v = iter.next().value;
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// returns <ndarray>
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arr = ndarray2array( v );
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// returns [ [ [ 5, 6 ], [ 7, 8 ] ] ]
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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][mdn-iterator-protocol] 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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</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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- If an environment supports `Symbol.iterator`, the returned iterator is iterable.
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- A returned iterator does **not** copy a provided [`ndarray`][@stdlib/ndarray/ctor]. To ensure iterable reproducibility, copy the input [`ndarray`][@stdlib/ndarray/ctor] **before** creating an iterator. Otherwise, any changes to the contents of input [`ndarray`][@stdlib/ndarray/ctor] will be reflected in the returned iterator.
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- In environments supporting `Symbol.iterator`, the function **explicitly** does **not** invoke an ndarray's `@@iterator` method, regardless of whether this method is defined.
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- Including the selected dimension as a singleton dimension can be useful when wanting to ensure that returned views remain [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes] with the input [`ndarray`][@stdlib/ndarray/ctor].
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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 array = require( '@stdlib/ndarray/array' );
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var zeroTo = require( '@stdlib/array/base/zero-to' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var nditerSelectDimension = require( '@stdlib/ndarray/iter/select-dimension' );
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// Define an input array:
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var x = array( zeroTo( 27 ), {
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'shape': [ 3, 3, 3 ]
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});
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// Create an iterator for iterating over matrices:
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var it = nditerSelectDimension( x, 0 );
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// Perform manual iteration...
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var v;
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while ( true ) {
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v = it.next();
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if ( v.done ) {
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break;
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}
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console.log( ndarray2array( v.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 related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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</section>
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<!-- /.related -->
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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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[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/ctor
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[@stdlib/ndarray/slice]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/slice
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[@stdlib/ndarray/base/broadcast-shapes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/base/broadcast-shapes
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<!-- <related-links> -->
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/ndarray/iter/select-dimension/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) 2024 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 isIteratorLike = require( '@stdlib/assert/is-iterator-like' );
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var isndarrayLike = require( '@stdlib/assert/is-ndarray-like' );
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var array = require( '@stdlib/ndarray/array' );
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var pkg = require( './../package.json' ).name;
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var nditerSelectDimension = require( './../lib' );
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// MAIN //
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bench( pkg, function benchmark( b ) {
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var iter;
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var x;
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var i;
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x = array( [ [ [ 1, 2, 3, 4 ] ] ] );
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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iter = nditerSelectDimension( x, 0 );
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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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});
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bench( pkg+'::iteration', function benchmark( b ) {
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var xbuf;
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var iter;
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var x;
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var z;
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var i;
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xbuf = [];
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xbuf.length = b.iterations + 1;
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x = array( xbuf, {
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'shape': [ xbuf.length, 1, 1 ],
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'dtype': 'generic',
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'copy': false
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});
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iter = nditerSelectDimension( x, 0 );
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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 ( typeof z !== 'object' ) {
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b.fail( 'should return an ndarray' );
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}
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}
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b.toc();
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if ( !isndarrayLike( z ) ) {
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b.fail( 'should return an ndarray' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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});

‎lib/node_modules/@stdlib/ndarray/iter/select-dimension/docs/repl.txt

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{{alias}}( x, dim[, options] )
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Returns an iterator which iterates over each view along a specified
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dimension.
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If an environment supports Symbol.iterator, the returned iterator is
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iterable.
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If an environment supports Symbol.iterator, the function explicitly does not
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invoke an ndarray's `@@iterator` method, regardless of whether this method
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is defined.
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Parameters
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----------
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x: ndarray
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Input ndarray for which to create the iterator.
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dim: integer
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Dimension index. If less than zero, the index is resolved relative to
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the last dimension, with the last dimension corresponding to the value
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`-1`.
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options: Object (optional)
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Options.
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options.readonly: boolean (optional)
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Boolean indicating whether returned ndarray views should be read-only.
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If the input ndarray is read-only, setting this option to `false` raises
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an exception. Default: true.
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options.keepdim: boolean (optional)
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Boolean indicating whether returned views should include the selected
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dimension as a singleton dimension. Including the selected dimension as
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a singleton dimension can be useful when wanting to ensure that returned
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views remain broadcast compatible with the input ndarray. Default:
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false.
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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 x = {{alias:@stdlib/ndarray/array}}( [ [ [ 1, 2 ], [ 3, 4 ] ] ] );
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> var it = {{alias}}( x, 0 );
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> var v = it.next().value;
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> {{alias:@stdlib/ndarray/to-array}}( v )
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[ [ 1, 2 ], [ 3, 4 ] ]
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See Also
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--------
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