npm package: @stdlib/array-base-unary4d-by
Description: Apply a unary function to each element retrieved from a four-dimensional nested input array according to a callback function and assign results to elements in a four-dimensional nested output array.
Author: The Stdlib Authors
Latest version: 0.1.1

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# unary4dBy

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

> Apply a unary function to each element retrieved from a four-dimensional nested input array according to a callback function and assign results to elements in a four-dimensional nested output array.

<section class="intro">

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/array-base-unary4d-by
```

</section>

<section class="usage">

## Usage

```javascript
var unary4dBy = require( '@stdlib/array-base-unary4d-by' );
```

#### unary4dBy( arrays, shape, fcn, clbk\[, thisArg] )

Applies a unary function to each element retrieved from a four-dimensional nested input array according to a callback function and assigns results to elements in a four-dimensional nested output array.

```javascript
var abs = require( '@stdlib/math-base-special-abs' );

function accessor( v ) {
    return v * 2.0;
}

var x = [ [ [ [ -1.0, -2.0 ], [ -3.0, -4.0 ] ] ] ];
var shape = [ 1, 1, 2, 2 ];

unary4dBy( [ x, x ], shape, abs, accessor );
// x => [ [ [ [ 2.0, 4.0 ], [ 6.0, 8.0 ] ] ] ]
```

The function accepts the following arguments:

-   **arrays**: array-like object containing one input nested array and one output nested array.
-   **shape**: array shape.
-   **fcn**: unary function to apply to callback return values.
-   **clbk**: callback function.
-   **thisArg**: callback function execution context (optional).

The invoked callback function is provided the following arguments:

-   **value**: array element.
-   **indices**: current array element indices.
-   **arrays**: input and output arrays.

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

<!-- eslint-disable no-invalid-this -->

```javascript
var abs = require( '@stdlib/math-base-special-abs' );

function accessor( v ) {
    this.count += 1;
    return v * 2.0;
}

var context = {
    'count': 0
};

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

var shape = [ 1, 1, 2, 2 ];

unary4dBy( [ x, y ], shape, abs, accessor, context );
// y => [ [ [ [ 2.0, 4.0 ], [ 6.0, 8.0 ] ] ] ]

var cnt = context.count;
// returns 4
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

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

    ```javascript
    var abs = require( '@stdlib/math-base-special-abs' );

    function accessor() {
        // No-op...
    }

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

    var shape = [ 1, 1, 2, 2 ];

    unary4dBy( [ x, y ], shape, abs, accessor );
    // y => [ [ [ [ 0.0, 0.0 ], [ 0.0, 0.0 ] ] ] ]
    ```

-   The function assumes that the input and output arrays have the same shape.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var bernoulli = require( '@stdlib/random-base-bernoulli' );
var filled4dBy = require( '@stdlib/array-base-filled4d-by' );
var zeros4d = require( '@stdlib/array-base-zeros4d' );
var abs = require( '@stdlib/math-base-special-abs' );
var unary4dBy = require( '@stdlib/array-base-unary4d-by' );

function accessor( v ) {
    // Randomly determine whether a value should be considered "missing":
    return ( bernoulli( 0.5 ) > 0 ) ? v : void 0;
}

var shape = [ 2, 2, 3, 3 ];

var x = filled4dBy( shape, discreteUniform( -100, 100 ) );
console.log( x );

var y = zeros4d( shape );
console.log( y );

unary4dBy( [ x, y ], shape, abs, accessor );
console.log( y );
```

</section>

<!-- /.examples -->

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<section class="related">

</section>

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<section class="main-repo" >

* * *

## 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].

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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