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# sliceAssign

> Assign element values from a broadcasted input [`ndarray`][@stdlib/ndarray/ctor] to corresponding elements in an output [`ndarray`][@stdlib/ndarray/ctor] view.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="usage">

## Usage

```javascript
var sliceAssign = require( '@stdlib/ndarray/slice-assign' );
```

#### sliceAssign( x, y, ...s\[, options] )

Assigns element values from a broadcasted input [`ndarray`][@stdlib/ndarray/ctor] to corresponding elements in an output [`ndarray`][@stdlib/ndarray/ctor] view.

```javascript
var Slice = require( '@stdlib/slice/ctor' );
var MultiSlice = require( '@stdlib/slice/multi' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var ndzeros = require( '@stdlib/ndarray/zeros' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

// Define an input array:
var buffer = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var shape = [ 3, 2 ];
var strides = [ 2, 1 ];
var offset = 0;

var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' );
// returns <ndarray>

var sh = x.shape;
// returns [ 3, 2 ]

var arr = ndarray2array( x );
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]

// Define an output array:
var y = ndzeros( [ 2, 3, 2 ], {
    'dtype': x.dtype
});

// Create a slice:
var s0 = null;
var s1 = new Slice( null, null, -1 );
var s2 = new Slice( null, null, -1 );
var s = new MultiSlice( s0, s1, s2 );
// returns <MultiSlice>

// Perform assignment:
var out = sliceAssign( x, y, s );
// returns <ndarray>

var bool = ( out === y );
// returns true

arr = ndarray2array( y );
// returns [ [ [ 6.0, 5.0 ], [ 4.0, 3.0 ], [ 2.0, 1.0 ] ], [ [ 6.0, 5.0 ], [ 4.0, 3.0 ], [ 2.0, 1.0 ] ] ]
```

The function accepts the following arguments:

-   **x**: input [`ndarray`][@stdlib/ndarray/ctor].
-   **y**: output [`ndarray`][@stdlib/ndarray/ctor].
-   **s**: a [`MultiSlice`][@stdlib/slice/multi] instance, an array of slice arguments, or slice arguments as separate arguments.
-   **options**: function options.

The function supports three (mutually exclusive) means for providing slice arguments:

1.  providing a single [`MultiSlice`][@stdlib/slice/multi] instance.
2.  providing a single array of slice arguments.
3.  providing slice arguments as separate arguments.

The following example demonstrates each invocation style achieving equivalent results.

```javascript
var Slice = require( '@stdlib/slice/ctor' );
var MultiSlice = require( '@stdlib/slice/multi' );
var scalar2ndarray = require( '@stdlib/ndarray/from-scalar' );
var ndzeros = require( '@stdlib/ndarray/zeros' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

// 1. Using a MultiSlice:
var x = scalar2ndarray( 10.0 );
var y = ndzeros( [ 2, 3 ] );

var s0 = 0;
var s1 = new Slice( 1, null, 1 );
var s = new MultiSlice( s0, s1 );
// returns <MultiSlice>

var out = sliceAssign( x, y, s );
// returns <ndarray>

var arr = ndarray2array( out );
// returns [ [ 0.0, 10.0, 10.0 ], [ 0.0, 0.0, 0.0 ] ]

// 2. Using an array of slice arguments:
x = scalar2ndarray( 10.0 );
y = ndzeros( [ 2, 3 ] );

out = sliceAssign( x, y, [ s0, s1 ] );
// returns <ndarray>

arr = ndarray2array( out );
// returns [ [ 0.0, 10.0, 10.0 ], [ 0.0, 0.0, 0.0 ] ]

// 3. Providing separate arguments:
x = scalar2ndarray( 10.0 );
y = ndzeros( [ 2, 3 ] );

out = sliceAssign( x, y, s0, s1 );
// returns <ndarray>

arr = ndarray2array( out );
// returns [ [ 0.0, 10.0, 10.0 ], [ 0.0, 0.0, 0.0 ] ]
```

The function supports the following `options`:

-   **strict**: boolean indicating whether to enforce strict bounds checking.

By default, the function throws an error when provided a slice which exceeds array bounds. To ignore slice indices exceeding array bounds, set the `strict` option to `false`.

```javascript
var Slice = require( '@stdlib/slice/ctor' );
var MultiSlice = require( '@stdlib/slice/multi' );
var scalar2ndarray = require( '@stdlib/ndarray/from-scalar' );
var ndzeros = require( '@stdlib/ndarray/zeros' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

// Define an input array:
var x = scalar2ndarray( 10.0 );

// Define an output array:
var y = ndzeros( [ 3, 2 ], {
    'dtype': x.dtype
});

// Create a slice:
var s0 = new Slice( 1, null, 1 );
var s1 = new Slice( 10, 20, 1 );
var s = new MultiSlice( s0, s1 );
// returns <MultiSlice>

// Perform assignment:
var out = sliceAssign( x, y, s, {
    'strict': false
});
// returns <ndarray>

var arr = ndarray2array( y );
// returns [ [ 0.0, 0.0 ], [ 0.0, 0.0 ], [ 0.0, 0.0 ] ]
```

</section>

<!-- /.usage -->

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

<section class="notes">

## Notes

-   An output [`ndarray`][@stdlib/ndarray/ctor] **must** be writable. If provided a **read-only** [`ndarray`][@stdlib/ndarray/ctor], the function throws an error.
-   A **slice argument** must be either a [`Slice`][@stdlib/slice/ctor], an integer, `null`, or `undefined`.
-   The number of slice dimensions must match the number of output array dimensions. Hence, if `y` is a zero-dimensional [`ndarray`][@stdlib/ndarray/ctor], then, if `s` is a [`MultiSlice`][@stdlib/slice/multi], `s` should be empty, and, if `s` is an array, `s` should not contain any slice arguments. Similarly, if `y` is a one-dimensional [`ndarray`][@stdlib/ndarray/ctor], then, if `s` is a [`MultiSlice`][@stdlib/slice/multi], `s` should have one slice dimension, and, if `s` is an array, `s` should contain a single slice argument. And so on and so forth.
-   The input [`ndarray`][@stdlib/ndarray/ctor] **must** be [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes] with the output [`ndarray`][@stdlib/ndarray/ctor] view.
-   The input [`ndarray`][@stdlib/ndarray/ctor] must have a [data type][@stdlib/ndarray/dtypes] which can be [safely cast][@stdlib/ndarray/safe-casts] to the output [`ndarray`][@stdlib/ndarray/ctor] data type. Floating-point data types (both real and complex) are allowed to downcast to a lower precision data type of the [same kind][@stdlib/ndarray/same-kind-casts] (e.g., element values from a `'float64'` input [`ndarray`][@stdlib/ndarray/ctor] can be assigned to corresponding elements in a `'float32'` output [`ndarray`][@stdlib/ndarray/ctor]).

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

<!-- eslint-disable new-cap -->

```javascript
var E = require( '@stdlib/slice/multi' );
var scalar2ndarray = require( '@stdlib/ndarray/from-scalar' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var ndzeros = require( '@stdlib/ndarray/zeros' );
var slice = require( '@stdlib/ndarray/slice' );
var sliceAssign = require( '@stdlib/ndarray/slice-assign' );

// Alias `null` to allow for more compact indexing expressions:
var _ = null;

// Create an output ndarray:
var y = ndzeros( [ 3, 3, 3 ] );

// Update each matrix...
var s1 = E( 0, _, _ );
sliceAssign( scalar2ndarray( 100 ), y, s1 );

var a1 = ndarray2array( slice( y, s1 ) );
// returns [ [ 100, 100, 100 ], [ 100, 100, 100 ], [ 100, 100, 100 ] ]

var s2 = E( 1, _, _ );
sliceAssign( scalar2ndarray( 200 ), y, s2 );

var a2 = ndarray2array( slice( y, s2 ) );
// returns [ [ 200, 200, 200 ], [ 200, 200, 200 ], [ 200, 200, 200 ] ]

var s3 = E( 2, _, _ );
sliceAssign( scalar2ndarray( 300 ), y, s3 );

var a3 = ndarray2array( slice( y, s3 ) );
// returns [ [ 300, 300, 300 ], [ 300, 300, 300 ], [ 300, 300, 300 ] ]

// Update the second rows in each matrix:
var s4 = E( _, 1, _ );
sliceAssign( scalar2ndarray( 400 ), y, s4 );

var a4 = ndarray2array( slice( y, s4 ) );
// returns [ [ 400, 400, 400 ], [ 400, 400, 400 ], [ 400, 400, 400 ] ]

// Update the second columns in each matrix:
var s5 = E( _, _, 1 );
sliceAssign( scalar2ndarray( 500 ), y, s5 );

var a5 = ndarray2array( slice( y, s5 ) );
// returns [ [ 500, 500, 500 ], [ 500, 500, 500 ], [ 500, 500, 500 ] ]

// Return the contents of the entire ndarray:
var a6 = ndarray2array( y );
/* returns
  [
    [
      [ 100, 500, 100 ],
      [ 400, 500, 400 ],
      [ 100, 500, 100 ]
    ],
    [
      [ 200, 500, 200 ],
      [ 400, 500, 400 ],
      [ 200, 500, 200 ]
    ],
    [
      [ 300, 500, 300 ],
      [ 400, 500, 400 ],
      [ 300, 500, 300 ]
    ]
  ]
*/
```

</section>

<!-- /.examples -->

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</section>

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

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/ndarray/array`][@stdlib/ndarray/array]</span><span class="delimiter">: </span><span class="description">multidimensional arrays.</span>
-   <span class="package-name">[`@stdlib/ndarray/ctor`][@stdlib/ndarray/ctor]</span><span class="delimiter">: </span><span class="description">multidimensional array constructor.</span>
-   <span class="package-name">[`@stdlib/ndarray/slice`][@stdlib/ndarray/slice]</span><span class="delimiter">: </span><span class="description">return a read-only view of an input ndarray.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[@stdlib/slice/ctor]: https://www.npmjs.com/package/@stdlib/slice-ctor

[@stdlib/slice/multi]: https://www.npmjs.com/package/@stdlib/slice-multi

[@stdlib/ndarray/base/broadcast-shapes]: https://github.com/stdlib-js/ndarray/tree/main/base/broadcast-shapes

[@stdlib/ndarray/safe-casts]: https://github.com/stdlib-js/ndarray/tree/main/safe-casts

[@stdlib/ndarray/same-kind-casts]: https://github.com/stdlib-js/ndarray/tree/main/same-kind-casts

[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes

[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor

<!-- <related-links> -->

[@stdlib/ndarray/array]: https://github.com/stdlib-js/ndarray/tree/main/array

[@stdlib/ndarray/slice]: https://github.com/stdlib-js/ndarray/tree/main/slice

<!-- </related-links> -->

</section>

<!-- /.links -->
