@stdlib/utils-async-group-by

Group values according to an indicator function.

https://github.com/stdlib-js/utils-async-group-by

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aggregate array async asynchronous collection group group-by groupby javascript node node-js nodejs partition split stdlib summarize util utilities utility utils

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Repository

Group values according to an indicator function.

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Host: GitHub
Owner: stdlib-js
License: apache-2.0
Language: JavaScript
Default Branch: main
Homepage: https://github.com/stdlib-js/stdlib
Size: 1 MB

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aggregate array async asynchronous collection group group-by groupby javascript node node-js nodejs partition split stdlib summarize util utilities utility utils

Created over 4 years ago · Last pushed 9 months ago

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We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

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To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

groupByAsync

Group values according to an indicator function.

## Installation ```bash npm install @stdlib/utils-async-group-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 groupByAsync = require( '@stdlib/utils-async-group-by' ); ``` #### groupByAsync( collection, \[options,] indicator, done ) Groups values according to an `indicator` function, which specifies which group an element in the input `collection` belongs to. ```javascript function indicator( value, next ) { setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, (value > 2000) ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var arr = [ 3000, 2500, 1000 ]; groupByAsync( arr, indicator, done ); /* => 1000 2500 3000 { 'true': [ 2500, 3000 ], 'false': [ 1000 ] } */ ``` The function accepts the following `options`: - **limit**: the maximum number of pending invocations at any one time. Default: `infinity`. - **series**: boolean indicating whether to sequentially invoke the `indicator` function for each `collection` element. If `true`, the function sets `options.limit=1`. Default: `false`. - **returns**: specifies the output format. If the option equals `'values'`, the function returns group results as element values. If the option equals `'indices'`, the function returns group results as element indices. If the option equals `'*'`, the function returns group results as both element indices and values. Default: `'values'`. - **thisArg**: the execution context for `indicator`. By default, the function returns group results as element values. To return element indices, set the `returns` option to `'indices'`. ```javascript function indicator( value, next ) { setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, (value > 2000) ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var arr = [ 3000, 2500, 1000 ]; var opts = { 'returns': 'indices' }; groupByAsync( arr, opts, indicator, done ); /* => 1000 2500 3000 { 'true': [ 1, 0 ], 'false': [ 2 ] } */ ``` To return index-value pairs, set the `returns` option to `'*'`. ```javascript function indicator( value, next ) { setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, (value > 2000) ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var arr = [ 3000, 2500, 1000 ]; var opts = { 'returns': '*' }; groupByAsync( arr, opts, indicator, done ); /* => 1000 2500 3000 { 'true': [ [ 1, 2500 ], [ 0, 3000 ] ], 'false': [ [ 2, 1000 ] ] } */ ``` By default, all elements are processed concurrently, which means that the function does **not** guarantee completion order. To process each `collection` element sequentially, set the `series` option to `true`. ```javascript function indicator( value, next ) { setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, (value > 2000) ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var arr = [ 3000, 2500, 1000 ]; var opts = { 'series': true }; groupByAsync( arr, opts, indicator, done ); /* => 3000 2500 1000 { 'true': [ 3000, 2500 ], 'false': [ 1000 ] } */ ``` To limit the maximum number of pending function invocations, set the `limit` option. ```javascript function indicator( value, next ) { setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, (value > 2000) ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var arr = [ 3000, 2500, 1000 ]; var opts = { 'limit': 2 }; groupByAsync( arr, opts, indicator, done ); /* => 2500 3000 1000 { 'true': [ 2500, 3000 ], 'false': [ 1000 ] } */ ``` To set the execution context of the `indicator` function, set the `thisArg` option. ```javascript function indicator( value, next ) { this.count += 1; setTimeout( onTimeout, value ); function onTimeout() { next( null, (value > 2000) ); } } var arr = [ 3000, 2500, 1000 ]; var context = { 'count': 0 }; var opts = { 'thisArg': context }; groupByAsync( arr, opts, indicator, done ); function done( error, result ) { if ( error ) { throw error; } console.log( result ); // => { 'true': [ 2500, 3000 ], 'false': [ 1000 ] } console.log( context.count ); // => 3 } ``` When invoked, the `indicator` function is provided a maximum of four arguments: - **value**: collection value. - **index**: collection index. - **collection**: the input `collection`. - **next**: a callback which should be called once the `indicator` function has finished processing a collection `value`. The actual number of provided arguments depends on function `length`. If the `indicator` function accepts two arguments, the `indicator` function is provided `value` and `next`. If the `indicator` function accepts three arguments, the `indicator` function is provided `value`, `index`, and `next`. For every other `indicator` function signature, the `indicator` function is provided all four arguments. ```javascript function indicator( value, i, collection, next ) { console.log( 'collection: %s. %d: %d', collection.join( ',' ), i, value ); setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, (value > 2000) ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var arr = [ 3000, 2500, 1000 ]; groupByAsync( arr, indicator, done ); /* => collection: 3000,2500,1000. 0: 3000 collection: 3000,2500,1000. 1: 2500 collection: 3000,2500,1000. 2: 1000 1000 2500 3000 { 'true': [ 2500, 3000 ], 'false': [ 1000 ] } */ ``` #### groupByAsync.factory( \[options,] indicator ) Returns a function which invokes an `indicator` function once for each element in a `collection`. ```javascript function indicator( value, next ) { setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, (value > 2000) ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var f = groupByAsync.factory( indicator ); var arr1 = [ 3000, 2500, 1000 ]; f( arr1, done ); /* => 1000 2500 3000 { 'true': [ 2500, 3000 ], 'false': [ 1000 ] } */ var arr2 = [ 300, 250, 100 ]; f( arr2, done ); /* => 100 250 300 { 'false': [ 100, 250, 300 ] } */ ``` The function accepts the same `options` as `groupByAsync()`.

## Notes - A `collection` may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`). - If a provided function calls the `next` callback with a truthy `error` argument, the function suspends execution and immediately calls the `done` callback for subsequent `error` handling. - The function does **not** support dynamic `collection` resizing. - The function does **not** skip `undefined` elements. - If provided an empty `collection`, the function calls the `done` callback with an empty `object` for the group results. - **Neither** `groupByAsync` nor the function returned by the `factory` method **guarantee** asynchronous execution. To guarantee asynchrony, wrap the `done` callback in a function which either executes at the end of the current stack (e.g., `nextTick`) or during a subsequent turn of the event loop (e.g., `setImmediate`, `setTimeout`). - The `group` returned by an `indicator` function should be a value which can be serialized as an `object` key. As a counterexample, ```javascript function indicator( value, next ) { setTimeout( onTimeout, value ); function onTimeout() { console.log( value ); next( null, {} ); } } function done( error, result ) { if ( error ) { throw error; } console.log( result ); } var arr = [ 3000, 2500, 1000 ]; groupByAsync( arr, indicator, done ); /* => 1000 2500 3000 { '[object Object]': [ 1000, 2500, 3000 ] } */ ``` while each group identifier is unique, all collection elements resolve to the same group because each group identifier serializes to the same string.

## Examples ```javascript var resolve = require( 'path' ).resolve; var readFile = require( '@stdlib/fs-read-file' ); var groupByAsync = require( '@stdlib/utils-async-group-by' ); var files = [ resolve( __dirname, 'package.json' ), resolve( __dirname, 'README.md' ), resolve( __dirname, 'beep.boop.md' ) ]; function done( error, result ) { if ( error ) { throw error; } console.log( result ); } function indicator( file, next ) { var opts = { 'encoding': 'utf8' }; readFile( file, opts, onFile ); function onFile( error ) { if ( error ) { return next( null, 'nonreadable' ); } next( null, 'readable' ); } } groupByAsync( files, indicator, done ); ```

* * * ## 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].

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  Standard library for JavaScript and Node.js.

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license: Apache-2.0 AND BSL-1.0

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npmjs.org: @stdlib/utils-async-group-by

Group values according to an indicator function.

Homepage: https://stdlib.io
License: Apache-2.0
Latest release: 0.2.2
published over 1 year ago

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