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https://github.com/stdlib-js/iter-unique-by-hash

Create an iterator which returns unique values according to a hash function.
https://github.com/stdlib-js/iter-unique-by-hash

dedupe deduplicate distinct hash iterable iterate iterator javascript node node-js nodejs stdlib uniq unique util utilities utility utils

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Create an iterator which returns unique values according to a hash function.

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README 

        



  

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# iterUniqueByHash



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



> Create an [iterator][mdn-iterator-protocol] which returns unique values according to a hash function.



## Installation



```bash

npm install @stdlib/iter-unique-by-hash

```



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 iterUniqueByHash = require( '@stdlib/iter-unique-by-hash' );

```



#### iterUniqueByHash( iterator, hashFcn\[, thisArg] )



Returns an [iterator][mdn-iterator-protocol] which returns unique values according to a hash function.



```javascript

var array2iterator = require( '@stdlib/array-to-iterator' );



function hashFcn( v ) {

    return v;

}



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



var it = iterUniqueByHash( src, hashFcn );

// returns 



var v = it.next().value;

// returns 2



v = it.next().value;

// returns 1



v = it.next().value;

// returns 4



v = it.next().value;

// returns 3



var bool = it.next().done;

// returns true

```



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][mdn-iterator-protocol] protocol-compliant object.



A hash function is provided one argument:



-   **v**: the current iterated value



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



```javascript

var array2iterator = require( '@stdlib/array-to-iterator' );



function hashFcn( v ) {

    this.count += 1;

    return JSON.stringify( v );

}



var values = [

    { 'v': 2 },

    { 'v': 1 },

    { 'v': 1 },

    { 'v': 2 },

    { 'v': 4 },

    { 'v': 3 },

    { 'v': 4 },

    { 'v': 3 }

];



var src = array2iterator( values );



var ctx = {

    'count': 0

};



var it = iterUniqueByHash( src, hashFcn, ctx );

// returns 



var v = it.next().value;

// returns { 'v': 2 }



v = it.next().value;

// returns { 'v': 1 }



v = it.next().value;

// returns { 'v': 4 }



v = it.next().value;

// returns { 'v': 3 }



var bool = it.next().done;

// returns true



bool = ( ctx.count > 0 );

// returns true

```



## Notes



-   A returned [iterator][mdn-iterator-protocol] internally buffers unique hashes and, thus, has `O(N)` memory requirements.

-   An iterated value is considered "unique" if a hash function returns a unique hash value for that iterated value. Beware that this _may_ result in unexpected behavior. Namely, only the **first** iterated value mapping to a particular hash function result is returned, even if subsequent values, while mapping to the same hash, are different. Accordingly, iteration order **does** matter.

-   If an environment supports `Symbol.iterator` **and** a provided [iterator][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.



## Examples



```javascript

var discreteUniform = require( '@stdlib/random-iter-discrete-uniform' );

var iterMap = require( '@stdlib/iter-map' );

var iterUniqueByHash = require( '@stdlib/iter-unique-by-hash' );



function mapFcn( v ) {

    return {

        'v': v

    };

}



function hashFcn( v ) {

    return JSON.stringify( v );

}



// Create a seeded iterator which can generate 1000 pseudorandom numbers:

var rand = discreteUniform( 1, 10, {

    'seed': 1234,

    'iter': 1000

});



// Create an iterator which maps each number to an object:

var miter = iterMap( rand, mapFcn );



// Create an iterator which returns unique (object) values:

var it = iterUniqueByHash( miter, hashFcn );



// Perform manual iteration...

var v;

while ( true ) {

    v = it.next();

    if ( v.done ) {

        break;

    }

    console.log( v.value );

}

```



* * *



## See Also



-   [`@stdlib/iter-unique`][@stdlib/iter/unique]: create an iterator which returns unique values.

-   [`@stdlib/iter-unique-by`][@stdlib/iter/unique-by]: create an iterator which returns unique values according to a predicate function.



* * *



## 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/iter-unique-by-hash.svg

[npm-url]: https://npmjs.org/package/@stdlib/iter-unique-by-hash



[test-image]: https://github.com/stdlib-js/iter-unique-by-hash/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/iter-unique-by-hash/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/iter-unique-by-hash/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/iter-unique-by-hash?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/iter-unique-by-hash/tree/deno

[deno-readme]: https://github.com/stdlib-js/iter-unique-by-hash/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/iter-unique-by-hash/tree/umd

[umd-readme]: https://github.com/stdlib-js/iter-unique-by-hash/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/iter-unique-by-hash/tree/esm

[esm-readme]: https://github.com/stdlib-js/iter-unique-by-hash/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/iter-unique-by-hash/blob/main/branches.md



[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/iter-unique-by-hash/main/LICENSE



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



[@stdlib/iter/unique]: https://github.com/stdlib-js/iter-unique



[@stdlib/iter/unique-by]: https://github.com/stdlib-js/iter-unique-by