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

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# sparsearray2iteratorRight

> Create an iterator from a sparse array-like object, iterating from right to left.

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## Usage

```javascript
var sparsearray2iteratorRight = require( '@stdlib/array/to-sparse-iterator-right' );
```

#### sparsearray2iteratorRight( src\[, mapFcn\[, thisArg]] )

Returns an iterator which iterates from right to left over each element in a sparse array-like `object`.

<!-- eslint-disable no-sparse-arrays -->

```javascript
var it = sparsearray2iteratorRight( [ 1, , , 4 ] );
// returns <Object>

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

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

var bool = it.next().done;
// returns true
```

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

-   **next**: function which returns an iterator 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 is finished.
-   **return**: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

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

<!-- eslint-disable no-sparse-arrays -->

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

var it = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn );
// returns <Object>

var v = it.next().value;
// returns 40.0

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

// ...
```

The invoked function is provided three arguments:

-   `value`: iterated value
-   `index`: iterated value index
-   `src`: source array-like object

<!-- eslint-disable no-sparse-arrays -->

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

var it = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn );
// returns <Object>

var v = it.next().value;
// returns 16

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

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

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

<!-- eslint-disable no-sparse-arrays -->

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

var ctx = {
    'count': 0
};

var it = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn, ctx );
// returns <Object>

var v = it.next().value;
// returns 40.0

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

var count = ctx.count;
// returns 2
```

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## Notes

-   If an environment supports `Symbol.iterator`, the returned iterator is iterable.
-   If provided a generic `array`, the returned iterator **ignores** holes (i.e., `undefined` values). To iterate over all generic `array` elements, use [`@stdlib/array/to-iterator-right`][@stdlib/array/to-iterator-right].
-   A returned iterator does **not** copy a provided array-like `object`. To ensure iterable reproducibility, copy a provided array-like `object` **before** creating an iterator. Otherwise, any changes to the contents of an array-like `object` will be reflected in the returned iterator.
-   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, invoke this method directly.

</section>

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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 sparsearray2iteratorRight = require( '@stdlib/array/to-sparse-iterator-right' );

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

// Create an array partially filled with random numbers:
var arr = new Array( 100 );
var i;
for ( i = 0; i < arr.length; i += 2 ) {
    arr[ i ] = randu();
}

// Create an iterator from the array which scales iterated values:
var it = sparsearray2iteratorRight( arr, scale );

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

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

</section>

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