npm package: @stdlib/strided-base-read-dataview
Description: Copy elements from an input strided DataView to elements in an output strided array.
Author: The Stdlib Authors
Latest version: 0.1.1

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# readDataView

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> Copy elements from an input strided [`DataView`][@stdlib/array/dataview] to elements in an output strided array.

<section class="intro">

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/strided-base-read-dataview
```

</section>

<section class="usage">

## Usage

```javascript
var readDataView = require( '@stdlib/strided-base-read-dataview' );
```

#### readDataView( N, view, strideView, out, strideOut, littleEndian )

Copies elements from an input strided [`DataView`][@stdlib/array/dataview] to elements in an output strided array.

```javascript
var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length );
var out = readDataView( x.length, view, 8, y, 1, true );
// e.g., returns <Float64Array>[ 1.0, 2.0, 3.0, 4.0 ]

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

The function accepts the following arguments:

-   **N**: number of indexed elements.
-   **view**: input [`DataView`][@stdlib/array/dataview].
-   **strideView**: index increment (in bytes) for `view`.
-   **out**: output strided array.
-   **strideOut**: index increment for `out`.
-   **littleEndian**: boolean indicating whether to store values in little-endian format.

The `N` and stride parameters determine which elements in `view` and `out` are accessed at runtime. For example, to index the first `N` elements of `view` in reverse order and to index every other value in `out`,

```javascript
var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length*2 );
var out = readDataView( x.length, view, -8, y, 2, true );
// e.g., returns <Float64Array>[ 4.0, 0.0, 3.0, 0.0, 2.0, 0.0, 1.0, 0.0 ]

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

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

```javascript
var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

// Initial output array:
var y0 = new Float64Array( x.length+1 );

// Create an offset view:
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var out = readDataView( x.length, view, 8, y1, 1, true );
// e.g., returns <Float64Array>[ 1.0, 2.0, 3.0, 4.0 ]

var bool = ( out === y1 );
// returns true
```

#### readDataView.ndarray( N, view, strideView, offsetView, out, strideOut, offsetOut, littleEndian )

Copies elements from an input strided [`DataView`][@stdlib/array/dataview] to elements in an output strided array using alternative indexing semantics.

```javascript
var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length );
var out = readDataView.ndarray( x.length, view, 8, 0, y, 1, 0, true );
// e.g., returns <Float64Array>[ 1.0, 2.0, 3.0, 4.0 ]

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

The function accepts the following additional arguments:

-   **offsetView**: starting index (in bytes) for `view`.
-   **offsetOut**: starting index for `out`.

While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to index the last `N` elements in `view` in reverse order and to index every other value in `out` starting from the second value,

```javascript
var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length*2 );
var out = readDataView.ndarray( x.length, view, -8, 24, y, 2, 1, true );
// e.g., returns <Float64Array>[ 0.0, 4.0, 0.0, 3.0, 0.0, 2.0, 0.0, 1.0 ]

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

</section>

<!-- /.usage -->

<section class="notes">

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var DataView = require( '@stdlib/array-dataview' );
var typedarray = require( '@stdlib/array-typed' );
var bytesPerElement = require( '@stdlib/ndarray-base-bytes-per-element' );
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var IS_LITTLE_ENDIAN = require( '@stdlib/assert-is-little-endian' );
var logEach = require( '@stdlib/console-log-each' );
var readDataView = require( '@stdlib/strided-base-read-dataview' );

// Specify the array data type:
var dtype = 'float64';

// Resolve the number of bytes per element:
var nbytes = bytesPerElement( dtype );

// Generate an array of random numbers:
var x = discreteUniform( 10, 0, 100, {
    'dtype': dtype
});

// Create a DataView:
var view = new DataView( x.buffer );

// Create an output array:
var out = typedarray( x.length, dtype );

// Read elements from the DataView according to host byte order:
readDataView( out.length, view, nbytes, out, 1, IS_LITTLE_ENDIAN );

// Print the results:
logEach( '%d -> %d', x, out );

// Read elements from the DataView according to the opposite byte order:
readDataView( out.length, view, nbytes, out, 1, !IS_LITTLE_ENDIAN );

// Print the results:
logEach( '%d -> %d', x, out );
```

</section>

<!-- /.examples -->

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<section class="related">

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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].

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---

## License

See [LICENSE][stdlib-license].


## Copyright

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

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