time-to-botec/squiggle/node_modules/@stdlib/array/to-strided-iterator/README.md

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# Strided Iterator

> Create an [iterator][mdn-iterator-protocol] from a strided array-like object.

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## Usage

```javascript
var stridedarray2iterator = require( '@stdlib/array/to-strided-iterator' );
```

#### stridedarray2iterator( N, src, stride, offset\[, mapFcn\[, thisArg]] )

Returns an [iterator][mdn-iterator-protocol] which iterates over elements in an array-like `object` according to specified stride parameters.

```javascript
var values = [ 1, 2, 3, 4, 5, 6, 7, 8 ];

var N = 4;
var stride = -2;
var offset = 6;

var it = stridedarray2iterator( N, values, stride, offset );
// returns <Object>

var v = it.next().value;
// returns 7

v = it.next().value;
// returns 5

v = it.next().value;
// returns 3

// ...
```

The returned [iterator][mdn-iterator-protocol] protocol-compliant object has the following properties:

-   **next**: function which returns an [iterator][mdn-iterator-protocol] protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the [iterator][mdn-iterator-protocol] is finished.
-   **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an iterator protocol-compliant object.

To invoke a function for each `src` value, provide a callback function.

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

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn );
// returns <Object>

var v = it.next().value;
// returns 10.0

v = it.next().value;
// returns 20.0

v = it.next().value;
// returns 30.0

// ...
```

The invoked function is provided four arguments:

-   `value`: iterated value
-   `index`: iterated value index
-   `n`: iteration count (zero-based)
-   `src`: source array-like object

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

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 4

v = it.next().value;
// returns 9

// ...
```

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

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

var ctx = {
    'count': 0
};

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn, ctx );
// returns <Object>

var v = it.next().value;
// returns 10.0

v = it.next().value;
// returns 20.0

v = it.next().value;
// returns 30.0

var count = ctx.count;
// returns 3
```

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## Notes

-   If an environment supports `Symbol.iterator`, the returned [iterator][mdn-iterator-protocol] is iterable.
-   If provided a generic `array`, the returned [iterator][mdn-iterator-protocol] does **not** ignore holes. To achieve greater performance for sparse arrays, use a custom [iterator][mdn-iterator-protocol].
-   A returned [iterator][mdn-iterator-protocol] does **not** copy a provided array-like `object`. To ensure iterable reproducibility, copy a provided array-like `object` **before** creating an [iterator][mdn-iterator-protocol]. Otherwise, any changes to the contents of an array-like `object` will be reflected in the returned [iterator][mdn-iterator-protocol].
-   In environments supporting `Symbol.iterator`, the function **explicitly** does **not** invoke an array's `@@iterator` method, regardless of whether this method is defined. To convert an array to an implementation defined [iterator][mdn-iterator-protocol], invoke this method directly.

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## Examples

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

```javascript
var Float64Array = require( '@stdlib/array/float64' );
var inmap = require( '@stdlib/utils/inmap' );
var randu = require( '@stdlib/random/base/randu' );
var stridedarray2iterator = require( '@stdlib/array/to-strided-iterator' );

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

// Create an array filled with random numbers:
var arr = inmap( new Float64Array( 100 ), randu );

// Create an iterator which scales every fourth value in reverse order:
var it = stridedarray2iterator( 25, arr, -4, 99, scale );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    console.log( v.value );
}
```

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[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol

</section>

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