npm package: @stdlib/ndarray-base-fill-by
Description: Fill an input ndarray according to a callback function.
Author: The Stdlib Authors
Latest version: 0.1.1

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# fillBy

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> Fill an input ndarray according to a callback function.

<section class="intro">

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/ndarray-base-fill-by
```

</section>

<section class="usage">

## Usage

```javascript
var fillBy = require( '@stdlib/ndarray-base-fill-by' );
```

#### fillBy( x, fcn\[, thisArg] )

Fills an input ndarray according to a callback function.

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

function fcn() {
    return 10.0;
}

var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ] );
// returns <ndarray>[ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ]

var out = fillBy( x, fcn );
// returns <ndarray>[ [ [ 10.0, 10.0 ] ], [ [ 10.0, 10.0 ] ], [ [ 10.0, 10.0 ] ] ]

var bool = ( out === x );
// returns true
```

The function accepts the following arguments:

-   **x**: array-like object containing an input ndarray.
-   **fcn**: callback function.
-   **thisArg**: callback function execution context (_optional_).

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

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

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

function fcn( value ) {
    return value * 10.0;
}

var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ] );
// returns <ndarray>[ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ]

var ctx = {
    'factor': 10.0
};

var out = fillBy( x, fcn, ctx );
// returns <ndarray>[ [ [ 10.0, 20.0 ] ], [ [ 30.0, 40.0 ] ], [ [ 50.0, 60.0 ] ] ]

var bool = ( out === x );
// returns true
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   A provided ndarray should be an object with the following properties:

    -   **dtype**: data type.
    -   **data**: data buffer.
    -   **shape**: dimensions.
    -   **strides**: stride lengths.
    -   **offset**: index offset.
    -   **order**: specifies whether an ndarray is row-major (C-style) or column major (Fortran-style).

-   The callback function is provided the following arguments:

    -   **value**: current array element.
    -   **indices**: current array element indices.
    -   **arr**: the input ndarray.

-   The function **mutates** the input ndarray.

-   The function assumes that each element in the underlying input ndarray data buffer has one, and only one, corresponding element in input ndarray view (i.e., a provided ndarray is not a broadcasted ndarray view).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var zeros = require( '@stdlib/ndarray-zeros' );
var fillBy = require( '@stdlib/ndarray-base-fill-by' );

// Create a zero-filled ndarray:
var x = zeros( [ 5, 2 ], {
    'dtype': 'generic'
});
console.log( ndarray2array( x ) );

// Fill the ndarray with random values:
fillBy( x, discreteUniform( -100, 100 ) );
console.log( ndarray2array( x ) );
```

</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].

#### Community

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

---

## License

See [LICENSE][stdlib-license].


## Copyright

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

</section>

<!-- /.stdlib -->

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