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Add utility to perform a map-reduce operation while iterating from right to left
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‎lib/node_modules/@stdlib/utils/map-reduce-right/README.md‎

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<!--
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@license Apache-2.0
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Copyright (c) 2022 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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# mapReduceRight
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> Perform a single-pass map-reduce operation against each element in an array while iterating from right to left and return the accumulated result.
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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 mapReduceRight = require( '@stdlib/utils/map-reduce-right' );
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```
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#### mapReduceRight( arr, initial, mapper, reducer\[, thisArg ] )
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Performs a map-reduce operation against each element in an array while iterating from right to left and returns the accumulated result.
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```javascript
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function square( value ) {
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return value * value;
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}
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function sum( accumulator, value ) {
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return accumulator + value;
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}
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var arr = [ 1, 2, 3, 4 ];
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var out = mapReduceRight( arr, 0, square, sum );
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// returns 30
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```
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The function accepts both array-like objects and [`ndarray`][@stdlib/ndarray/ctor]-like objects.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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function square( value ) {
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return value * value;
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}
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function sum( accumulator, value ) {
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return accumulator + value;
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}
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var opts = {
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'dtype': 'generic'
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};
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var arr = array( [ [ 1, 2, 3 ], [ 4, 5, 6 ] ], opts );
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var out = mapReduceRight( arr, 0, square, sum );
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// returns 91
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```
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The mapping function is provided the following arguments:
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- **value**: array element.
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- **index**: element index.
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- **arr**: input array.
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The reducing function is provided the following arguments:
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- **accumulator**: accumulated value.
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- **value**: result of applying the mapping function to the current array element.
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- **index**: element index.
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- **arr**: input array.
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To set the `this` context when invoking the reducing function, provide a `thisArg`.
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<!-- eslint-disable no-invalid-this -->
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```javascript
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function square( value ) {
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return value * value;
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}
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function sum( accumulator, value ) {
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this.count += 1;
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return accumulator + value;
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}
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var arr = [ 1, 2, 3, 4 ];
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var ctx = {
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'count': 0
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};
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var out = mapReduceRight( arr, 0, square, sum, ctx );
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// returns 30
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var mean = out / ctx.count;
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// returns 7.5
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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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- The function supports array-like objects exposing getters and setters for array element access (e.g., [`Complex64Array`][@stdlib/array/complex64], [`Complex128Array`][@stdlib/array/complex128], etc).
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```javascript
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var Complex64Array = require( '@stdlib/array/complex64' );
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var Complex64 = require( '@stdlib/complex/float32' );
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var cceil = require( '@stdlib/math/base/special/cceil' );
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var realf = require( '@stdlib/complex/realf' );
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var imagf = require( '@stdlib/complex/imagf' );
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function sum( acc, z ) {
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var re1 = realf( acc );
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var im1 = imagf( acc );
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var re2 = realf( z );
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var im2 = imagf( z );
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return new Complex64( re1+re2, im1+im2 );
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}
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var x = new Complex64Array( [ 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5 ] );
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var v = mapReduceRight( x, new Complex64( 0.0, 0.0 ), cceil, sum );
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// returns <Complex64>
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var re = realf( v );
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// returns 20.0
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var im = imagf( v );
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// returns 24.0
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```
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- For [`ndarray`][@stdlib/ndarray/ctor]-like objects, the function performs a single-pass map-reduce operation over the entire input [`ndarray`][@stdlib/ndarray/ctor] (i.e., higher-order [`ndarray`][@stdlib/ndarray/ctor] dimensions are flattened to a single-dimension).
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- When applying a function to [`ndarray`][@stdlib/ndarray/ctor]-like objects, performance will be best for [`ndarray`][@stdlib/ndarray/ctor]-like objects which are single-segment contiguous.
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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 filledarrayBy = require( '@stdlib/array/filled-by' );
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var discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory;
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var naryFunction = require( '@stdlib/utils/nary-function' );
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var add = require( '@stdlib/math/base/ops/add' );
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var abs = require( '@stdlib/math/base/special/abs' );
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var array = require( '@stdlib/ndarray/array' );
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var mapReduceRight = require( '@stdlib/utils/map-reduce-right' );
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function fill( i ) {
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var rand = discreteUniform( -10*(i+1), 10*(i+1) );
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return filledarrayBy( 10, 'generic', rand );
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}
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// Create a two-dimensional ndarray (i.e., a matrix):
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var x = array( filledarrayBy( 10, 'generic', fill ), {
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'dtype': 'generic',
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'flatten': true
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});
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// Create an explicit unary function:
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var f1 = naryFunction( abs, 1 );
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// Create an explicit binary function:
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var f2 = naryFunction( add, 2 );
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// Compute the sum of absolute values:
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var out = mapReduceRight( x, 0, f1, f2 );
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console.log( 'x:' );
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console.log( x.data );
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console.log( 'sum: %d', 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 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
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[@stdlib/array/complex64]: https://github.com/stdlib-js/stdlib
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[@stdlib/array/complex128]: https://github.com/stdlib-js/stdlib
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/utils/map-reduce-right/benchmark/benchmark.array.js‎

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2022 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 pow = require( '@stdlib/math/base/special/pow' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var filled = require( '@stdlib/array/base/filled' );
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var add = require( '@stdlib/math/base/ops/add' );
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var abs = require( '@stdlib/math/base/special/abs' );
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var pkg = require( './../package.json' ).name;
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var mapReduceRight = require( './../lib' );
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// FUNCTIONS //
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/**
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* Creates a benchmark function.
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*
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* @private
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* @param {PositiveInteger} len - array length
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* @returns {Function} benchmark function
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*/
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function createBenchmark( len ) {
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var x = filled( -3.0, len );
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return benchmark;
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/**
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* Benchmark function.
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*
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* @private
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* @param {Benchmark} b - benchmark instance
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*/
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function benchmark( b ) {
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var out;
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var i;
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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out = mapReduceRight( x, 0.0, abs, add );
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if ( isnan( out ) ) {
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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( out ) ) {
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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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}
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}
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// MAIN //
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/**
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* Main execution sequence.
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*
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* @private
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*/
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function main() {
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var len;
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var min;
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var max;
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var f;
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var i;
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min = 1; // 10^min
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max = 6; // 10^max
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for ( i = min; i <= max; i++ ) {
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len = pow( 10, i );
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f = createBenchmark( len );
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bench( pkg+'::array:len='+len, f );
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}
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}
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main();

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