@stdlib/strided/base/read-dataview/README.md

Strided.

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# readDataView

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

<section class="intro">

</section>

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<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>

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<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>

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<section class="related">

</section>

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<section class="links">

[@stdlib/array/dataview]: https://www.npmjs.com/package/@stdlib/array-dataview

</section>

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