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https://github.com/stdlib-js/array-to-sparse-iterator-right

Create an iterator from a sparse array-like object, iterating from right to left.
https://github.com/stdlib-js/array-to-sparse-iterator-right

arr array holes iter iterate iteration iterator javascript node node-js nodejs sparse stdlib typed typed-array util utilities utility utils

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

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README 

        



  

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# sparsearray2iteratorRight



[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] 



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



## Installation



```bash

npm install @stdlib/array-to-sparse-iterator-right

```



Alternatively,



-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).



The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.



To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.



## 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`.



```javascript

var it = sparsearray2iteratorRight( [ 1, , , 4 ] );

// returns 



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.



```javascript

function fcn( v ) {

    return v * 10.0;

}



var it = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn );

// returns 



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.



```javascript

function fcn( v, i ) {

    return v * (i+1);

}



var it = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn );

// returns 



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`.



```javascript

function fcn( v ) {

    this.count += 1;

    return v * 10.0;

}



var ctx = {

    'count': 0

};



var it = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn, ctx );

// returns 



var v = it.next().value;

// returns 40.0



v = it.next().value;

// returns 20.0



var count = ctx.count;

// returns 2

```



## 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.

-   The returned iterator supports array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array-complex64`][@stdlib/array/complex64]).



## Examples



```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 );

}

```



* * *



## See Also



-   [`@stdlib/array-from-iterator`][@stdlib/array/from-iterator]: create (or fill) an array from an iterator.

-   [`@stdlib/array-to-iterator-right`][@stdlib/array/to-iterator-right]: create an iterator from an array-like object, iterating from right to left.

-   [`@stdlib/array-to-sparse-iterator`][@stdlib/array/to-sparse-iterator]: create an iterator from a sparse array-like object.



* * *



## 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].



#### Community



[![Chat][chat-image]][chat-url]



---



## License



See [LICENSE][stdlib-license].



## Copyright



Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].



[npm-image]: http://img.shields.io/npm/v/@stdlib/array-to-sparse-iterator-right.svg

[npm-url]: https://npmjs.org/package/@stdlib/array-to-sparse-iterator-right



[test-image]: https://github.com/stdlib-js/array-to-sparse-iterator-right/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/array-to-sparse-iterator-right/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/array-to-sparse-iterator-right/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/array-to-sparse-iterator-right?branch=main



[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im



[stdlib]: https://github.com/stdlib-js/stdlib



[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors



[umd]: https://github.com/umdjs/umd

[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules



[deno-url]: https://github.com/stdlib-js/array-to-sparse-iterator-right/tree/deno

[deno-readme]: https://github.com/stdlib-js/array-to-sparse-iterator-right/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/array-to-sparse-iterator-right/tree/umd

[umd-readme]: https://github.com/stdlib-js/array-to-sparse-iterator-right/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/array-to-sparse-iterator-right/tree/esm

[esm-readme]: https://github.com/stdlib-js/array-to-sparse-iterator-right/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/array-to-sparse-iterator-right/blob/main/branches.md



[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/array-to-sparse-iterator-right/main/LICENSE



[@stdlib/array/complex64]: https://github.com/stdlib-js/array-complex64



[@stdlib/array/from-iterator]: https://github.com/stdlib-js/array-from-iterator



[@stdlib/array/to-iterator-right]: https://github.com/stdlib-js/array-to-iterator-right



[@stdlib/array/to-sparse-iterator]: https://github.com/stdlib-js/array-to-sparse-iterator