npm package: @stdlib/array-base-at4d
Description: Return an element from a four-dimensional nested array.
Author: The Stdlib Authors
Latest version: 0.2.3

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# at4d

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

> Return an element from a four-dimensional nested array.

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<section class="intro">

</section>

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<section class="installation">

## Installation

```bash
npm install @stdlib/array-base-at4d
```

</section>

<section class="usage">

## Usage

```javascript
var at4d = require( '@stdlib/array-base-at4d' );
```

#### at4d( x, i0, i1, i2, i3 )

Returns an element from a four-dimensional nested array.

```javascript
var x = [ [ [ [ 1, 2 ], [ 3, 4 ] ] ] ];

var out = at4d( x, 0, 0, 0, 1 );
// returns 2

out = at4d( x, 0, 0, 1, 0 );
// returns 3
```

The function accepts the following arguments:

-   **x**: four-dimensional nested input array.
-   **i0**: first dimension index.
-   **i1**: second dimension index.
-   **i2**: third dimension index.
-   **i3**: fourth dimension index.

</section>

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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   Negative indices are resolved relative to the last element along the respective dimension, with the last element corresponding to `-1`.
-   If provided out-of-bounds indices, the function always returns `undefined`.

</section>

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<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var papply = require( '@stdlib/utils-papply' );
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var filled4dBy = require( '@stdlib/array-base-filled4d-by' );
var quaternary4d = require( '@stdlib/array-base-quaternary4d' );
var zeros4d = require( '@stdlib/array-base-zeros4d' );
var at4d = require( '@stdlib/array-base-at4d' );

var shape = [ 2, 2, 4, 4 ];

// Define a nested input array:
var x = filled4dBy( shape, discreteUniform( -100, 100 ) );
console.log( x );

// Define arrays containing random index values:
var i0 = filled4dBy( shape, discreteUniform( -shape[0], shape[0]-1 ) );
console.log( i0 );

var i1 = filled4dBy( shape, discreteUniform( -shape[1], shape[1]-1 ) );
console.log( i1 );

var i2 = filled4dBy( shape, discreteUniform( -shape[2], shape[2]-1 ) );
console.log( i2 );

var i3 = filled4dBy( shape, discreteUniform( -shape[3], shape[3]-1 ) );
console.log( i3 );

// Define an output array:
var out = zeros4d( shape );
console.log( out );

// Fill the output array with randomly selected values from the input array:
quaternary4d( [ i0, i1, i2, i3, out ], shape, papply( at4d, x ) );
console.log( out );
```

</section>

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* * *

## 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

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---

## License

See [LICENSE][stdlib-license].


## Copyright

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

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