@stdlib/iter/to-array-view/README.md

Standard iterator utilities.

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# iterator2arrayview

> Fill an array-like object view with values returned from an iterator.

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## Usage

```javascript
var iterator2arrayview = require( '@stdlib/iter/to-array-view' );
```

#### iterator2arrayview( iterator, dest\[, begin\[, end]]\[, mapFcn\[, thisArg]] )

Fills an array-like `object` view with values returned from an `iterator`.

```javascript
var Uint8Array = require( '@stdlib/array/uint8' );
var array2iterator = require( '@stdlib/array/to-iterator' );

var iter = array2iterator( [ 1, 2, 3, 4 ] );

var arr = iterator2arrayview( iter, new Uint8Array( 10 ) );
// returns <Uint8Array>[ 1, 2, 3, 4, 0, 0, 0, 0, 0, 0 ]
```

By default, the function begins filling from the first element of a provided array-like `object`. To specify an alternative starting index, provide a `begin` argument (zero-based and inclusive).

```javascript
var Uint8Array = require( '@stdlib/array/uint8' );
var array2iterator = require( '@stdlib/array/to-iterator' );

var iter = array2iterator( [ 1, 2, 3, 4 ] );

var arr = iterator2arrayview( iter, new Uint8Array( 10 ), 3 );
// returns <Uint8Array>[ 0, 0, 0, 1, 2, 3, 4, 0, 0, 0 ]
```

If `begin` is less than `0`, the starting index is resolved relative to the last element of the provided array-like `object`. For example, the following achieves the same behavior as the previous example

```javascript
var Uint8Array = require( '@stdlib/array/uint8' );
var array2iterator = require( '@stdlib/array/to-iterator' );

var iter = array2iterator( [ 1, 2, 3, 4 ] );

var arr = iterator2arrayview( iter, new Uint8Array( 10 ), -7 );
// returns <Uint8Array>[ 0, 0, 0, 1, 2, 3, 4, 0, 0, 0 ]
```

By default, the function assumes that a view extends through the last element of a provided array-like `object`. To specify an alternative last view element, provide an `end` argument (zero-based and non-inclusive).

```javascript
var Uint8Array = require( '@stdlib/array/uint8' );
var array2iterator = require( '@stdlib/array/to-iterator' );

var iter = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] );

var arr = iterator2arrayview( iter, new Uint8Array( 10 ), 0, 4 );
// returns <Uint8Array>[ 1, 2, 3, 4, 0, 0, 0, 0, 0, 0 ]
```

If `end` is less than `0`, the last view element is resolved relative to the last element of the provided array-like `object`. For example, the following achieves the same behavior as the previous example

```javascript
var Uint8Array = require( '@stdlib/array/uint8' );
var array2iterator = require( '@stdlib/array/to-iterator' );

var iter = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] );

var arr = iterator2arrayview( iter, new Uint8Array( 10 ), 0, -6 );
// returns <Uint8Array>[ 1, 2, 3, 4, 0, 0, 0, 0, 0, 0 ]
```

To invoke a function for each iterated value, provide a callback function.

```javascript
var Float64Array = require( '@stdlib/array/float64' );
var array2iterator = require( '@stdlib/array/to-iterator' );

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

var iter = array2iterator( [ 1, 2, 3, 4 ] );

var arr = iterator2arrayview( iter, new Float64Array( 4 ), fcn );
// returns <Float64Array>[ 10.0, 20.0, 30.0, 40.0 ]
```

The invoked function is provided three arguments:

-   **value**: iterated value.
-   **index**: destination index.
-   **n**: iteration count (zero-based).

```javascript
var Uint8Array = require( '@stdlib/array/uint8' );
var array2iterator = require( '@stdlib/array/to-iterator' );

function fcn( v, i ) {
    return v * (i+1);
}

var iter = array2iterator( [ 1, 2, 3, 4 ] );

var arr = iterator2arrayview( iter, new Uint8Array( 4 ), fcn );
// returns <Uint8Array>[ 1, 4, 9, 16 ]
```

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

```javascript
var Float64Array = require( '@stdlib/array/float64' );
var randu = require( '@stdlib/random/iter/randu' );

function fcn( v ) {
    this.count += 1;
    return v * 10.0;
}

var ctx = {
    'count': 0
};

var arr = iterator2arrayview( randu(), new Float64Array( 10 ), fcn, ctx );
// returns <Float64Array>

var count = ctx.count;
// returns 10
```

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

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## Notes

-   Iteration stops when an output array view is full **or** an iterator finishes; whichever comes first.
-   The function supports output array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array/complex64`][@stdlib/array/complex64]).

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## Examples

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

```javascript
var Float64Array = require( '@stdlib/array/float64' );
var randu = require( '@stdlib/random/iter/randu' );
var iterator2arrayview = require( '@stdlib/iter/to-array-view' );

function scale( v, i ) {
    return v * (i+1);
}

// Create an iterator for generating uniformly distributed pseudorandom numbers:
var it = randu();

// Fill an array view with scaled iterator values:
var arr = iterator2arrayview( it, new Float64Array( 100 ), 40, 60, scale );

var i;
for ( i = 0; i < arr.length; i++ ) {
    console.log( arr[ i ] );
}
```

</section>

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* * *

## See Also

-   <span class="package-name">[`@stdlib/array/from-iterator`][@stdlib/array/from-iterator]</span><span class="delimiter">: </span><span class="description">create (or fill) an array from an iterator.</span>
-   <span class="package-name">[`@stdlib/array/to-view-iterator`][@stdlib/array/to-view-iterator]</span><span class="delimiter">: </span><span class="description">create an iterator from an array-like object view.</span>
-   <span class="package-name">[`@stdlib/iter/to-array-view-right`][@stdlib/iter/to-array-view-right]</span><span class="delimiter">: </span><span class="description">fill an array-like object view from right to left with values returned from an iterator.</span>

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[@stdlib/array/complex64]: https://www.npmjs.com/package/@stdlib/array-complex64

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

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

[@stdlib/array/to-view-iterator]: https://www.npmjs.com/package/@stdlib/array-to-view-iterator

[@stdlib/iter/to-array-view-right]: https://github.com/stdlib-js/iter/tree/main/to-array-view-right

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

</section>

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