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# fillBy

> Fill an input ndarray according to a callback function.

<section class="intro">

</section>

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<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>

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<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 -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

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<section class="links">

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</section>

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