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https://github.com/stdlib-js/stats-base-nanmax-by

Calculate the maximum value of a strided array via a callback function, ignoring NaN values.
https://github.com/stdlib-js/stats-base-nanmax-by

array domain extent extremes javascript math mathematics max maximum node node-js nodejs range statistics stats stdlib strided strided-array

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Calculate the maximum value of a strided array via a callback function, ignoring NaN values.

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README 

        



  

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# nanmaxBy



[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] 



> Calculate the maximum value of a strided array via a callback function, ignoring `NaN` values.



## Installation



```bash

npm install @stdlib/stats-base-nanmax-by

```



Alternatively,



-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).



The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.



To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.



## Usage



```javascript

var nanmaxBy = require( '@stdlib/stats-base-nanmax-by' );

```



#### nanmaxBy( N, x, stride, clbk\[, thisArg] )



Calculates the maximum value of strided array `x` via a callback function, ignoring `NaN` values.



```javascript

function accessor( v ) {

    return v * 2.0;

}



var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, NaN, 0.0, -1.0, -3.0, NaN ];



var v = nanmaxBy( x.length, x, 1, accessor );

// returns 8.0

```



The function has the following parameters:



-   **N**: number of indexed elements.

-   **x**: input [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions). 

-   **stride**: index increment.

-   **clbk**: callback function.

-   **thisArg**: execution context (_optional_).



The invoked callback is provided four arguments:



-   **value**: array element.

-   **aidx**: array index.

-   **sidx**: strided index (`offset + aidx*stride`).

-   **array**: input array/collection.



To set the callback execution context, provide a `thisArg`.



```javascript

function accessor( v ) {

    this.count += 1;

    return v * 2.0;

}



var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, NaN, 0.0, -1.0, -3.0, NaN ];



var context = {

    'count': 0

};



var v = nanmaxBy( x.length, x, 1, accessor, context );

// returns 8.0



var cnt = context.count;

// returns 10

```



The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to access every other element



```javascript

var floor = require( '@stdlib/math-base-special-floor' );



function accessor( v ) {

    return v * 2.0;

}



var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0, NaN, NaN ];

var N = floor( x.length / 2 );



var v = nanmaxBy( N, x, 2, accessor );

// returns 8.0

```



Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.



```javascript

var Float64Array = require( '@stdlib/array-float64' );

var floor = require( '@stdlib/math-base-special-floor' );



function accessor( v ) {

    return v * 2.0;

}



// Initial array...

var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );



// Create an offset view...

var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var N = floor( x0.length/2 );



// Access every other element...

var v = nanmaxBy( N, x1, 2, accessor );

// returns -4.0

```



#### nanmaxBy.ndarray( N, x, stride, offset, clbk\[, thisArg] )



Calculates the maximum value of strided array `x` via a callback function, ignoring `NaN` values and using alternative indexing semantics.



```javascript

function accessor( v ) {

    return v * 2.0;

}



var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, NaN, 0.0, -1.0, -3.0, NaN ];



var v = nanmaxBy.ndarray( x.length, x, 1, 0, accessor );

// returns 8.0

```



The function has the following additional parameters:



-   **offset**: starting index.



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`



```javascript

function accessor( v ) {

    return v * 2.0;

}



var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];



var v = nanmaxBy.ndarray( 3, x, 1, x.length-3, accessor );

// returns 10.0

```



## Notes



-   If `N <= 0`, both functions return `NaN`.

-   A provided callback function should return a numeric value.

-   If a provided callback function returns `NaN`, the value is ignored.

-   If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is ignored.

-   When possible, prefer using [`dnanmax`][@stdlib/stats/base/dnanmax], [`snanmax`][@stdlib/stats/base/snanmax], and/or [`nanmax`][@stdlib/stats/base/nanmax], as, depending on the environment, these interfaces are likely to be significantly more performant.



## Examples



```javascript

var discreteUniform = require( '@stdlib/random-base-discrete-uniform' );

var randu = require( '@stdlib/random-base-randu' );

var filledarrayBy = require( '@stdlib/array-filled-by' );

var nanmaxBy = require( '@stdlib/stats-base-nanmax-by' );



function fill() {

    if ( randu() < 0.2 ) {

        return NaN;

    }

    return discreteUniform( -50, 50 );

}



function accessor( v ) {

    return v * 2.0;

}



var x = filledarrayBy( 10, 'float64', fill );

console.log( x );



var v = nanmaxBy( x.length, x, 1, accessor );

console.log( v );

```



* * *



## See Also



-   [`@stdlib/stats-base/dnanmax`][@stdlib/stats/base/dnanmax]: calculate the maximum value of a double-precision floating-point strided array, ignoring NaN values.

-   [`@stdlib/stats-base/max-by`][@stdlib/stats/base/max-by]: calculate the maximum value of a strided array via a callback function.

-   [`@stdlib/stats-base/nanmax`][@stdlib/stats/base/nanmax]: calculate the maximum value of a strided array, ignoring NaN values.

-   [`@stdlib/stats-base/nanmin-by`][@stdlib/stats/base/nanmin-by]: calculate the minimum value of a strided array via a callback function, ignoring NaN values.

-   [`@stdlib/stats-base/snanmax`][@stdlib/stats/base/snanmax]: calculate the maximum value of a single-precision floating-point strided array, ignoring NaN values.



* * *



## Notice



This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.



For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].



#### Community



[![Chat][chat-image]][chat-url]



---



## License



See [LICENSE][stdlib-license].



## Copyright



Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].



[npm-image]: http://img.shields.io/npm/v/@stdlib/stats-base-nanmax-by.svg

[npm-url]: https://npmjs.org/package/@stdlib/stats-base-nanmax-by



[test-image]: https://github.com/stdlib-js/stats-base-nanmax-by/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/stats-base-nanmax-by/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/stats-base-nanmax-by/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/stats-base-nanmax-by?branch=main



[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im



[stdlib]: https://github.com/stdlib-js/stdlib



[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors



[umd]: https://github.com/umdjs/umd

[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules



[deno-url]: https://github.com/stdlib-js/stats-base-nanmax-by/tree/deno

[deno-readme]: https://github.com/stdlib-js/stats-base-nanmax-by/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/stats-base-nanmax-by/tree/umd

[umd-readme]: https://github.com/stdlib-js/stats-base-nanmax-by/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/stats-base-nanmax-by/tree/esm

[esm-readme]: https://github.com/stdlib-js/stats-base-nanmax-by/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/stats-base-nanmax-by/blob/main/branches.md



[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/stats-base-nanmax-by/main/LICENSE



[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array



[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray



[@stdlib/stats/base/dnanmax]: https://github.com/stdlib-js/stats-base-dnanmax



[@stdlib/stats/base/max-by]: https://github.com/stdlib-js/stats-base-max-by



[@stdlib/stats/base/nanmax]: https://github.com/stdlib-js/stats-base-nanmax



[@stdlib/stats/base/nanmin-by]: https://github.com/stdlib-js/stats-base-nanmin-by



[@stdlib/stats/base/snanmax]: https://github.com/stdlib-js/stats-base-snanmax