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array-base-group-entries-by

Group element entries according to an indicator function.

https://github.com/stdlib-js/array-base-group-entries-by

Science Score: 44.0%

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aggregate array base data entries group group-by groupby indices javascript node node-js nodejs partition split stdlib structure summarize types
Last synced: 4 months ago · JSON representation ·

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Group element entries according to an indicator function.

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aggregate array base data entries group group-by groupby indices javascript node node-js nodejs partition split stdlib structure summarize types
Created almost 2 years ago · Last pushed 6 months ago
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README.md

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groupEntriesBy

NPM version Build Status Coverage Status <!-- dependencies -->

Group element entries according to an indicator function.

## Installation ```bash npm install @stdlib/array-base-group-entries-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 groupEntriesBy = require( '@stdlib/array-base-group-entries-by' ); ``` #### groupEntriesBy( x, indicator\[, thisArg] ) Groups element entries according to an indicator function. ```javascript function indicator( v ) { return v[ 0 ]; } var x = [ 'beep', 'boop', 'foo', 'bar' ]; var out = groupEntriesBy( x, indicator ); // returns { 'b': [ [ 0, 'beep' ], [ 1, 'boop' ], [ 3, 'bar' ] ], 'f': [ [ 2, 'foo' ] ] } ``` An `indicator` function is provided the following arguments: - **value**: current array element. - **index**: current array element index. - **arr**: input array. To set the `indicator` function execution context, provide a `thisArg`. ```javascript function indicator( v ) { this.count += 1; return v[ 0 ]; } var x = [ 'beep', 'boop', 'foo', 'bar' ]; var context = { 'count': 0 }; var out = groupEntriesBy( x, indicator, context ); // returns { 'b': [ [ 0, 'beep' ], [ 1, 'boop' ], [ 3, 'bar' ] ], 'f': [ [ 2, 'foo' ] ] } var cnt = context.count; // returns 4 ```
## Notes - The value returned by an `indicator` function should be a value which can be serialized as an object key. As a counterexample, ```javascript function indicator( v ) { return {}; } var x = [ 'beep', 'boop', 'foo', 'bar' ]; var out = groupEntriesBy( x, indicator ); // returns { '[object Object]': [ [ 0, 'beep' ], [ 1, 'boop' ], [ 2, 'foo' ], [ 3, 'bar' ] ] } ``` while each group identifier is unique, all input array elements resolve to the same group because each group identifier serializes to the same string.
## Examples ```javascript var discreteUniform = require( '@stdlib/random-array-discrete-uniform' ); var take = require( '@stdlib/array-base-take-indexed' ); var groupEntriesBy = require( '@stdlib/array-base-group-entries-by' ); function indicator( v ) { // Use the first letter of each element to define groups: return v[ 0 ]; } // Define an initial array of values: var values = [ 'beep', 'boop', 'foo', 'bar', 'woot', 'woot' ]; // Sample from the initial array to generate a random collection: var indices = discreteUniform( 100, 0, values.length-1, { 'dtype': 'generic' }); var x = take( values, indices ); // returns [...] // Group the values: var out = groupEntriesBy( x, indicator ); // returns {...} console.log( out ); ```
* * * ## 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.

Citation (CITATION.cff) 

cff-version: 1.2.0
title: stdlib
message: >-
  If you use this software, please cite it using the
  metadata from this file.

type: software

authors:
  - name: The Stdlib Authors
    url: https://github.com/stdlib-js/stdlib/graphs/contributors

repository-code: https://github.com/stdlib-js/stdlib
url: https://stdlib.io

abstract: |
  Standard library for JavaScript and Node.js.

keywords:
  - JavaScript
  - Node.js
  - TypeScript
  - standard library
  - scientific computing
  - numerical computing
  - statistical computing

license: Apache-2.0 AND BSL-1.0

date-released: 2016

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