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feat: add stats/strided/max-by
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‎lib/node_modules/@stdlib/stats/strided/max-by/README.md

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<!--
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@license Apache-2.0
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Copyright (c) 2020 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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# maxBy
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> Calculate the maximum value of a strided array via a callback function.
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<section class="usage">
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## Usage
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```javascript
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var maxBy = require( '@stdlib/stats/strided/max-by' );
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```
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#### maxBy( N, x, strideX, clbk\[, thisArg] )
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Computes the maximum value of a strided array via a callback function.
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```javascript
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function accessor( v ) {
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return v * 2.0;
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}
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var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
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var v = maxBy( x.length, x, 1, accessor );
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// returns 8.0
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```
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The function has the following parameters:
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- **N**: number of indexed elements.
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- **x**: input [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions).
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- **strideX**: stride length for `x`.
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- **clbk**: callback function.
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- **thisArg**: execution context (_optional_).
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The invoked callback is provided four arguments:
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- **value**: array element.
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- **aidx**: array index.
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- **sidx**: strided index (`offset + aidx*stride`).
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- **array**: input array/collection.
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To set the callback execution context, provide a `thisArg`.
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```javascript
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function accessor( v ) {
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this.count += 1;
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return v * 2.0;
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}
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var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
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var context = {
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'count': 0
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};
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var v = maxBy( x.length, x, 1, accessor, context );
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// returns 8.0
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var cnt = context.count;
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// returns 8
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```
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The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to access every other element
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```javascript
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function accessor( v ) {
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return v * 2.0;
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}
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var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
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var v = maxBy( 4, x, 2, accessor );
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// returns 8.0
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```
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Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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function accessor( v ) {
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return v * 2.0;
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}
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// Initial array...
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var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
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// Create an offset view...
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var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
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// Access every other element...
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var v = maxBy( 3, x1, 2, accessor );
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// returns -4.0
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```
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#### maxBy.ndarray( N, x, strideX, offsetX, clbk\[, thisArg] )
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Computes the maximum value of a strided array via a callback function and using alternative indexing semantics.
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```javascript
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function accessor( v ) {
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return v * 2.0;
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}
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var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
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var v = maxBy.ndarray( x.length, x, 1, 0, accessor );
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// returns 8.0
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```
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The function has the following additional parameters:
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- **offsetX**: starting index.
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While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameter supports indexing semantics based on a starting index. For example, to access only the last three elements of `x`
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```javascript
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function accessor( v ) {
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return v * 2.0;
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}
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var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];
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var v = maxBy.ndarray( 3, x, 1, x.length-3, accessor );
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// returns 10.0
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- If `N <= 0`, both functions return `NaN`.
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- A provided callback function should return a numeric value.
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- If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is **ignored**.
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- Both functions support array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array/base/accessor`][@stdlib/array/base/accessor]).
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- When possible, prefer using [`dmax`][@stdlib/stats/strided/dmax], [`smax`][@stdlib/stats/strided/smax], and/or [`max`][@stdlib/stats/base/max], as, depending on the environment, these interfaces are likely to be significantly more performant.
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</section>
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<!-- /.notes -->
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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 discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var maxBy = require( '@stdlib/stats/strided/max-by' );
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function accessor( v ) {
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return v * 2.0;
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}
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var x = discreteUniform( 10, -50, 50, {
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'dtype': 'float64'
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});
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console.log( x );
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var v = maxBy( x.length, x, 1, accessor );
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console.log( v );
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```
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</section>
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<!-- /.examples -->
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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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* * *
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## See Also
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- <span class="package-name">[`@stdlib/stats/strided/dmax`][@stdlib/stats/strided/dmax]</span><span class="delimiter">: </span><span class="description">calculate the maximum value of a double-precision floating-point strided array.</span>
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- <span class="package-name">[`@stdlib/stats/base/max`][@stdlib/stats/base/max]</span><span class="delimiter">: </span><span class="description">calculate the maximum value of a strided array.</span>
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- <span class="package-name">[`@stdlib/stats/base/min-by`][@stdlib/stats/base/min-by]</span><span class="delimiter">: </span><span class="description">calculate the minimum value of a strided array via a callback function.</span>
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- <span class="package-name">[`@stdlib/stats/base/nanmax-by`][@stdlib/stats/base/nanmax-by]</span><span class="delimiter">: </span><span class="description">calculate the maximum value of a strided array via a callback function, ignoring NaN values.</span>
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- <span class="package-name">[`@stdlib/stats/strided/smax`][@stdlib/stats/strided/smax]</span><span class="delimiter">: </span><span class="description">calculate the maximum value of a single-precision floating-point strided array.</span>
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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-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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[@stdlib/array/base/accessor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/base/accessor
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<!-- <related-links> -->
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[@stdlib/stats/strided/dmax]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/strided/dmax
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[@stdlib/stats/base/max]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/max
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[@stdlib/stats/base/min-by]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/min-by
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[@stdlib/stats/base/nanmax-by]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/nanmax-by
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[@stdlib/stats/strided/smax]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/strided/smax
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/stats/strided/max-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) 2020 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 uniform = require( '@stdlib/random/array/uniform' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var pkg = require( './../package.json' ).name;
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var maxBy = require( './../lib/main.js' );
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// VARIABLES //
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var options = {
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'dtype': 'generic'
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};
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// FUNCTIONS //
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/**
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* Accessor function.
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*
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* @private
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* @param {number} value - array element
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* @returns {number} accessed value
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*/
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function accessor( value ) {
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return value * 2.0;
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}
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/**
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* Create 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 = uniform( len, -10, 10, options );
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return benchmark;
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function benchmark( b ) {
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var y;
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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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y = maxBy( x.length, x, 1, accessor );
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if ( isnan( y ) ) {
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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( y ) ) {
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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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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+':len='+len, f );
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}
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}
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main();

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