https://github.com/stdlib-js/iter-dedupe-by
Create an iterator which removes consecutive values that resolve to the same value according to a provided function.
https://github.com/stdlib-js/iter-dedupe-by
compress dedupe deduplicate deduplication duplicate iterable iterate iteration iterator javascript node node-js nodejs stdlib uniq unique util utilities utility utils
Last synced: 9 months ago
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Create an iterator which removes consecutive values that resolve to the same value according to a provided function.
- Host: GitHub
- URL: https://github.com/stdlib-js/iter-dedupe-by
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-14T17:05:07.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2025-07-28T00:40:47.000Z (10 months ago)
- Last Synced: 2025-07-28T02:30:26.637Z (10 months ago)
- Topics: compress, dedupe, deduplicate, deduplication, duplicate, iterable, iterate, iteration, iterator, javascript, node, node-js, nodejs, stdlib, uniq, unique, util, utilities, utility, utils
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 1.04 MB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
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README
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# iterDedupeBy
[![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 removes consecutive values that resolve to the same value according to a provided function.
## Installation
```bash
npm install @stdlib/iter-dedupe-by
```
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 iterDedupeBy = require( '@stdlib/iter-dedupe-by' );
```
#### iterDedupeBy( iterator, \[limit,] fcn )
Returns an [iterator][mdn-iterator-protocol] which removes consecutive values that resolve to the same value according to a provided function.
```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );
function fcn( v ) {
return v;
}
var arr = array2iterator( [ 1, 1, 2, 3, 3, 3, 4, 4 ] );
var it = iterDedupeBy( arr, fcn );
// returns
var v = it.next().value;
// returns 1
v = it.next().value;
// returns 2
v = it.next().value;
// returns 3
v = it.next().value;
// returns 4
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.
The callback function is provided five arguments:
- **curr**: current source iterated value.
- **sprev**: previous source iterated value.
- **dprev**: previous downstream iterated value.
- **index**: source iteration index (zero-based).
- **acc**: previous resolved value.
The returned [iterator][mdn-iterator-protocol] removes **consecutive** values which resolve to the same value and does **not** return globally "unique" values.
```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );
function fcn( v ) {
return v;
}
var arr = array2iterator( [ 1, 1, 2, 1, 1, 2 ] );
var it = iterDedupeBy( arr, fcn );
// returns
var v = it.next().value;
// returns 1
v = it.next().value;
// returns 2
v = it.next().value;
// returns 1
v = it.next().value;
// returns 2
var bool = it.next().done;
// returns true
```
To specify the number of allowed consecutive duplicated values, provide a `limit` argument.
```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );
function fcn( v ) {
return v;
}
var arr = array2iterator( [ 1, 1, 2, 3, 3, 3, 3, 4, 4, 4 ] );
var it = iterDedupeBy( arr, 2, fcn );
// returns
var v = it.next().value;
// returns 1
v = it.next().value;
// returns 1
v = it.next().value;
// returns 2
v = it.next().value;
// returns 3
v = it.next().value;
// returns 3
v = it.next().value;
// returns 4
v = it.next().value;
// returns 4
var bool = it.next().done;
// returns true
```
## Notes
- 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 randi = require( '@stdlib/random-iter-discrete-uniform' );
var iterDedupe = require( '@stdlib/iter-dedupe' );
var iterDedupeBy = require( '@stdlib/iter-dedupe-by' );
function fcn( curr, sprev, dprev, i, acc ) {
if ( curr < dprev ) {
return 1;
}
if ( curr === dprev ) {
return acc; // ensures that duplicate values are removed
}
// curr > dprev
return -1;
}
// Create a seeded iterator for generating pseudorandom integers:
var rand = randi( 1, 10, {
'seed': 1234,
'iter': 100
});
// Create an iterator which removes consecutive duplicated values:
var deduped = iterDedupe( rand );
// Create an iterator which forces consecutive values to follow an alternating less than, greater than pattern:
var it = iterDedupeBy( deduped, fcn );
// Perform manual iteration...
var v;
while ( true ) {
v = it.next();
if ( v.done ) {
break;
}
console.log( v.value );
}
```
* * *
## See Also
- [`@stdlib/iter-dedupe`][@stdlib/iter/dedupe]: create an iterator which removes consecutive duplicated values.
- [`@stdlib/iter-unique`][@stdlib/iter/unique]: create an iterator which returns unique values.
* * *
## 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 © 2016-2025. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/iter-dedupe-by.svg
[npm-url]: https://npmjs.org/package/@stdlib/iter-dedupe-by
[test-image]: https://github.com/stdlib-js/iter-dedupe-by/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/iter-dedupe-by/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/iter-dedupe-by/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/iter-dedupe-by?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-dedupe-by/tree/deno
[deno-readme]: https://github.com/stdlib-js/iter-dedupe-by/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/iter-dedupe-by/tree/umd
[umd-readme]: https://github.com/stdlib-js/iter-dedupe-by/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/iter-dedupe-by/tree/esm
[esm-readme]: https://github.com/stdlib-js/iter-dedupe-by/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/iter-dedupe-by/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/iter-dedupe-by/main/LICENSE
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
[@stdlib/iter/dedupe]: https://github.com/stdlib-js/iter-dedupe
[@stdlib/iter/unique]: https://github.com/stdlib-js/iter-unique