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feat: add ndarray/reverse-dimension
PR-URL: #8186 Closes: stdlib-js/metr-issue-tracker#99 Ref: #2656 Co-authored-by: Athan Reines <kgryte@gmail.com> Reviewed-by: Athan Reines <kgryte@gmail.com>
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<!--
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@license Apache-2.0
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Copyright (c) 2025 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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# reverseDimension
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> Return a **read-only** view of an input [`ndarray`][@stdlib/ndarray/ctor] in which the order of elements along a specified dimension is reversed.
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro section element. -->
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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 reverseDimension = require( '@stdlib/ndarray/reverse-dimension' );
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```
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#### reverseDimension( x, dim )
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Returns a read-only view of an input [`ndarray`][@stdlib/ndarray/ctor] in which the order of elements along a specified dimension is reversed.
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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( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ], {
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'shape': [ 3, 2 ]
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});
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// returns <ndarray>
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var arr = ndarray2array( x );
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// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]
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var y = reverseDimension( x, 0 );
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// returns <ndarray>
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arr = ndarray2array( y );
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// returns [ [ 5.0, 6.0 ], [ 3.0, 4.0 ], [ 1.0, 2.0 ] ]
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```
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The function accepts the following arguments:
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- **x**: input ndarray.
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- **dim**: index of dimension along which to reverse elements. If provided an integer less than zero, the dimension index is resolved relative to the last dimension, with the last dimension corresponding to the value `-1`.
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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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</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 uniform = require( '@stdlib/random/uniform' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var reverseDimension = require( '@stdlib/ndarray/reverse-dimension' );
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var x = uniform( [ 3, 3, 3 ], -10.0, 10.0 );
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console.log( ndarray2array( x ) );
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var y = reverseDimension( x, 0 );
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console.log( ndarray2array( y ) );
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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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[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/ctor
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<!-- <related-links> -->
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<!-- </related-links> -->
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</section>
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<!-- /.links -->
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2025 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 isndarrayLike = require( '@stdlib/assert/is-ndarray-like' );
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var empty = require( '@stdlib/ndarray/empty' );
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var pkg = require( './../package.json' ).name;
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var reverseDimension = require( './../lib' );
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// MAIN //
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bench( pkg+'::1d', function benchmark( b ) {
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var values;
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var v;
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var i;
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/* eslint-disable object-curly-newline, stdlib/line-closing-bracket-spacing */
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values = [
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empty( [ 2 ], { 'dtype': 'float64' } ),
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empty( [ 2 ], { 'dtype': 'float32' } ),
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empty( [ 2 ], { 'dtype': 'int32' } ),
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empty( [ 2 ], { 'dtype': 'complex128' } ),
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empty( [ 2 ], { 'dtype': 'generic' } )
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];
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/* eslint-enable object-curly-newline, stdlib/line-closing-bracket-spacing */
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = reverseDimension( values[ i%values.length ], 0 );
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if ( typeof v !== '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( v ) ) {
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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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});
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bench( pkg+'::2d,dim=0', function benchmark( b ) {
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var values;
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var v;
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var i;
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/* eslint-disable object-curly-newline, stdlib/line-closing-bracket-spacing */
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values = [
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empty( [ 2, 2 ], { 'dtype': 'float64' } ),
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empty( [ 2, 2 ], { 'dtype': 'float32' } ),
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empty( [ 2, 2 ], { 'dtype': 'int32' } ),
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empty( [ 2, 2 ], { 'dtype': 'complex128' } ),
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empty( [ 2, 2 ], { 'dtype': 'generic' } )
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];
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/* eslint-enable object-curly-newline, stdlib/line-closing-bracket-spacing */
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = reverseDimension( values[ i%values.length ], 0 );
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if ( typeof v !== '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( v ) ) {
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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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});
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bench( pkg+'::2d,dim=1', function benchmark( b ) {
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var values;
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var v;
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var i;
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/* eslint-disable object-curly-newline, stdlib/line-closing-bracket-spacing */
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values = [
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empty( [ 2, 2 ], { 'dtype': 'float64' } ),
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empty( [ 2, 2 ], { 'dtype': 'float32' } ),
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empty( [ 2, 2 ], { 'dtype': 'int32' } ),
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empty( [ 2, 2 ], { 'dtype': 'complex128' } ),
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empty( [ 2, 2 ], { 'dtype': 'generic' } )
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];
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/* eslint-enable object-curly-newline, stdlib/line-closing-bracket-spacing */
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = reverseDimension( values[ i%values.length ], 1 );
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if ( typeof v !== '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( v ) ) {
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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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});
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bench( pkg+'::3d,dim=0', function benchmark( b ) {
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var values;
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var v;
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var i;
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/* eslint-disable object-curly-newline, stdlib/line-closing-bracket-spacing */
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values = [
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empty( [ 2, 2, 2 ], { 'dtype': 'float64' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'float32' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'int32' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'complex128' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'generic' } )
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];
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/* eslint-enable object-curly-newline, stdlib/line-closing-bracket-spacing */
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = reverseDimension( values[ i%values.length ], 0 );
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if ( typeof v !== '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( v ) ) {
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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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});
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bench( pkg+'::3d,dim=1', function benchmark( b ) {
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var values;
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var v;
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var i;
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/* eslint-disable object-curly-newline, stdlib/line-closing-bracket-spacing */
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values = [
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empty( [ 2, 2, 2 ], { 'dtype': 'float64' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'float32' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'int32' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'complex128' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'generic' } )
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];
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/* eslint-enable object-curly-newline, stdlib/line-closing-bracket-spacing */
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = reverseDimension( values[ i%values.length ], 1 );
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if ( typeof v !== '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( v ) ) {
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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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});
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bench( pkg+'::3d,dim=2', function benchmark( b ) {
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var values;
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var v;
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var i;
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/* eslint-disable object-curly-newline, stdlib/line-closing-bracket-spacing */
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values = [
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empty( [ 2, 2, 2 ], { 'dtype': 'float64' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'float32' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'int32' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'complex128' } ),
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empty( [ 2, 2, 2 ], { 'dtype': 'generic' } )
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];
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/* eslint-enable object-curly-newline, stdlib/line-closing-bracket-spacing */
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = reverseDimension( values[ i%values.length ], 2 );
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if ( typeof v !== '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( v ) ) {
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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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});
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{{alias}}( x, dim )
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Returns a read-only view of an input ndarray in which the order of elements
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along a specified dimension is reversed.
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Parameters
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----------
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x: ndarray
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Input array.
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dim: integer
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Index of dimension to reverse. If provided an integer less than zero,
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the dimension index is resolved relative to the last dimension, with the
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last dimension corresponding to the value `-1`.
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Returns
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-------
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out: ndarray
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A read-only view of an input ndarray in which the order of elements
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along a specified dimension is reversed.
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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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<ndarray>
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> {{alias:@stdlib/ndarray/to-array}}( x )
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[ [ 1, 2 ], [ 3, 4 ] ]
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> var y = {{alias}}( x, 0 )
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<ndarray>
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> {{alias:@stdlib/ndarray/to-array}}( y )
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[ [ 3, 4 ], [ 1, 2 ] ]
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See Also
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--------

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