{"id":26286381,"url":"https://github.com/stdlib-js/utils-map-reduce-right","last_synced_at":"2025-07-16T01:35:33.016Z","repository":{"id":41374090,"uuid":"451030168","full_name":"stdlib-js/utils-map-reduce-right","owner":"stdlib-js","description":"Perform a single-pass map-reduce operation against each element in an array while iterating from right to left and return the accumulated result.","archived":false,"fork":false,"pushed_at":"2025-04-07T00:43:01.000Z","size":2869,"stargazers_count":2,"open_issues_count":0,"forks_count":0,"subscribers_count":3,"default_branch":"main","last_synced_at":"2025-06-13T19:19:09.557Z","etag":null,"topics":["accumulate","accumulation","accumulator","aggregate","iterate","javascript","map","map-reduce","node","node-js","nodejs","reduce","reducer","reduction","stdlib","transform","util","utilities","utility","utils"],"latest_commit_sha":null,"homepage":"https://github.com/stdlib-js/stdlib","language":"JavaScript","has_issues":false,"has_wiki":null,"has_pages":null,"mirror_url":null,"source_name":null,"license":"apache-2.0","status":null,"scm":"git","pull_requests_enabled":true,"icon_url":"https://github.com/stdlib-js.png","metadata":{"files":{"readme":"README.md","changelog":"CHANGELOG.md","contributing":"CONTRIBUTING.md","funding":null,"license":"LICENSE","code_of_conduct":"CODE_OF_CONDUCT.md","threat_model":null,"audit":null,"citation":"CITATION.cff","codeowners":null,"security":"SECURITY.md","support":null,"governance":null,"roadmap":null,"authors":null,"dei":null,"publiccode":null,"codemeta":null,"zenodo":null},"funding":{"github":["stdlib-js"],"open_collective":"stdlib","tidelift":"npm/@stdlib/stdlib"}},"created_at":"2022-01-23T07:08:04.000Z","updated_at":"2025-04-07T00:34:12.000Z","dependencies_parsed_at":"2024-03-01T07:24:30.092Z","dependency_job_id":"f5d61a5f-63fd-42fb-ae33-48b610e94598","html_url":"https://github.com/stdlib-js/utils-map-reduce-right","commit_stats":{"total_commits":30,"total_committers":1,"mean_commits":30.0,"dds":0.0,"last_synced_commit":"e50c78abe4f291d3026e4d70fedf2f269fa49b7d"},"previous_names":[],"tags_count":13,"template":false,"template_full_name":null,"purl":"pkg:github/stdlib-js/utils-map-reduce-right","repository_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/stdlib-js%2Futils-map-reduce-right","tags_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/stdlib-js%2Futils-map-reduce-right/tags","releases_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/stdlib-js%2Futils-map-reduce-right/releases","manifests_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/stdlib-js%2Futils-map-reduce-right/manifests","owner_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners/stdlib-js","download_url":"https://codeload.github.com/stdlib-js/utils-map-reduce-right/tar.gz/refs/heads/main","sbom_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/stdlib-js%2Futils-map-reduce-right/sbom","host":{"name":"GitHub","url":"https://github.com","kind":"github","repositories_count":265282418,"owners_count":23739928,"icon_url":"https://github.com/github.png","version":null,"created_at":"2022-05-30T11:31:42.601Z","updated_at":"2022-07-04T15:15:14.044Z","host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":["accumulate","accumulation","accumulator","aggregate","iterate","javascript","map","map-reduce","node","node-js","nodejs","reduce","reducer","reduction","stdlib","transform","util","utilities","utility","utils"],"created_at":"2025-03-14T20:22:11.372Z","updated_at":"2025-07-16T01:35:32.968Z","avatar_url":"https://github.com/stdlib-js.png","language":"JavaScript","funding_links":["https://github.com/sponsors/stdlib-js","https://opencollective.com/stdlib","https://tidelift.com/funding/github/npm/@stdlib/stdlib"],"categories":[],"sub_categories":[],"readme":"\u003c!--\n\n@license Apache-2.0\n\nCopyright (c) 2022 The Stdlib Authors.\n\nLicensed under the Apache License, Version 2.0 (the \"License\");\nyou may not use this file except in compliance with the License.\nYou may obtain a copy of the License at\n\n   http://www.apache.org/licenses/LICENSE-2.0\n\nUnless required by applicable law or agreed to in writing, software\ndistributed under the License is distributed on an \"AS IS\" BASIS,\nWITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\nSee the License for the specific language governing permissions and\nlimitations under the License.\n\n--\u003e\n\n\n\u003cdetails\u003e\n  \u003csummary\u003e\n    About stdlib...\n  \u003c/summary\u003e\n  \u003cp\u003eWe 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.\u003c/p\u003e\n  \u003cp\u003eThe library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.\u003c/p\u003e\n  \u003cp\u003eWhen you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.\u003c/p\u003e\n  \u003cp\u003eTo join us in bringing numerical computing to the web, get started by checking us out on \u003ca href=\"https://github.com/stdlib-js/stdlib\"\u003eGitHub\u003c/a\u003e, and please consider \u003ca href=\"https://opencollective.com/stdlib\"\u003efinancially supporting stdlib\u003c/a\u003e. We greatly appreciate your continued support!\u003c/p\u003e\n\u003c/details\u003e\n\n# mapReduceRight\n\n[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] \u003c!-- [![dependencies][dependencies-image]][dependencies-url] --\u003e\n\n\u003e Perform a single-pass map-reduce operation against each element in an array while iterating from right to left and return the accumulated result.\n\n\u003c!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. --\u003e\n\n\u003csection class=\"intro\"\u003e\n\n\u003c/section\u003e\n\n\u003c!-- /.intro --\u003e\n\n\u003c!-- Package usage documentation. --\u003e\n\n\u003csection class=\"installation\"\u003e\n\n## Installation\n\n```bash\nnpm install @stdlib/utils-map-reduce-right\n```\n\nAlternatively,\n\n-   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]).\n-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).\n-   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]).\n\nThe [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.\n\nTo 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.\n\n\u003c/section\u003e\n\n\u003csection class=\"usage\"\u003e\n\n## Usage\n\n```javascript\nvar mapReduceRight = require( '@stdlib/utils-map-reduce-right' );\n```\n\n#### mapReduceRight( arr, initial, mapper, reducer\\[, thisArg ] )\n\nPerforms a map-reduce operation against each element in an array while iterating from right to left and returns the accumulated result.\n\n```javascript\nfunction square( value ) {\n    return value * value;\n}\n\nfunction sum( accumulator, value ) {\n    return accumulator + value;\n}\n\nvar arr = [ 1, 2, 3, 4 ];\n\nvar out = mapReduceRight( arr, 0, square, sum );\n// returns 30\n```\n\nThe function accepts both array-like objects and [`ndarray`][@stdlib/ndarray/ctor]-like objects.\n\n```javascript\nvar array = require( '@stdlib/ndarray-array' );\n\nfunction square( value ) {\n    return value * value;\n}\n\nfunction sum( accumulator, value ) {\n    return accumulator + value;\n}\n\nvar opts = {\n    'dtype': 'generic'\n};\nvar arr = array( [ [ 1, 2, 3 ], [ 4, 5, 6 ] ], opts );\n\nvar out = mapReduceRight( arr, 0, square, sum );\n// returns 91\n```\n\nThe mapping function is provided the following arguments:\n\n-   **value**: array element.\n-   **index**: element index.\n-   **arr**: input array.\n\nThe reducing function is provided the following arguments:\n\n-   **accumulator**: accumulated value.\n-   **value**: result of applying the mapping function to the current array element.\n-   **index**: element index.\n-   **arr**: input array.\n\nTo set the `this` context when invoking the reducing function, provide a `thisArg`.\n\n\u003c!-- eslint-disable no-invalid-this --\u003e\n\n```javascript\nfunction square( value ) {\n    return value * value;\n}\n\nfunction sum( accumulator, value ) {\n    this.count += 1;\n    return accumulator + value;\n}\n\nvar arr = [ 1, 2, 3, 4 ];\n\nvar ctx = {\n    'count': 0\n};\n\nvar out = mapReduceRight( arr, 0, square, sum, ctx );\n// returns 30\n\nvar mean = out / ctx.count;\n// returns 7.5\n```\n\n\u003c/section\u003e\n\n\u003c!-- /.usage --\u003e\n\n\u003c!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. --\u003e\n\n\u003csection class=\"notes\"\u003e\n\n## Notes\n\n-   The function supports array-like objects exposing getters and setters for array element access (e.g., [`Complex64Array`][@stdlib/array/complex64], [`Complex128Array`][@stdlib/array/complex128], etc).\n\n    ```javascript\n    var Complex64Array = require( '@stdlib/array-complex64' );\n    var Complex64 = require( '@stdlib/complex-float32-ctor' );\n    var cceil = require( '@stdlib/math-base-special-cceil' );\n    var realf = require( '@stdlib/complex-float32-real' );\n    var imagf = require( '@stdlib/complex-float32-imag' );\n\n    function sum( acc, z ) {\n        var re1 = realf( acc );\n        var im1 = imagf( acc );\n        var re2 = realf( z );\n        var im2 = imagf( z );\n        return new Complex64( re1+re2, im1+im2 );\n    }\n\n    var x = new Complex64Array( [ 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5 ] );\n\n    var v = mapReduceRight( x, new Complex64( 0.0, 0.0 ), cceil, sum );\n    // returns \u003cComplex64\u003e\n\n    var re = realf( v );\n    // returns 20.0\n\n    var im = imagf( v );\n    // returns 24.0\n    ```\n\n-   For [`ndarray`][@stdlib/ndarray/ctor]-like objects, the function performs a single-pass map-reduce operation over the entire input [`ndarray`][@stdlib/ndarray/ctor] (i.e., higher-order [`ndarray`][@stdlib/ndarray/ctor] dimensions are flattened to a single-dimension).\n\n-   When applying a function to [`ndarray`][@stdlib/ndarray/ctor]-like objects, performance will be best for [`ndarray`][@stdlib/ndarray/ctor]-like objects which are single-segment contiguous.\n\n\u003c/section\u003e\n\n\u003c!-- /.notes --\u003e\n\n\u003c!-- Package usage examples. --\u003e\n\n\u003csection class=\"examples\"\u003e\n\n## Examples\n\n\u003c!-- eslint no-undef: \"error\" --\u003e\n\n```javascript\nvar filledarrayBy = require( '@stdlib/array-filled-by' );\nvar discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;\nvar naryFunction = require( '@stdlib/utils-nary-function' );\nvar add = require( '@stdlib/number-float64-base-add' );\nvar abs = require( '@stdlib/math-base-special-abs' );\nvar array = require( '@stdlib/ndarray-array' );\nvar mapReduceRight = require( '@stdlib/utils-map-reduce-right' );\n\nfunction fill( i ) {\n    var rand = discreteUniform( -10*(i+1), 10*(i+1) );\n    return filledarrayBy( 10, 'generic', rand );\n}\n\n// Create a two-dimensional ndarray (i.e., a matrix):\nvar x = array( filledarrayBy( 10, 'generic', fill ), {\n    'dtype': 'generic',\n    'flatten': true\n});\n\n// Create an explicit unary function:\nvar f1 = naryFunction( abs, 1 );\n\n// Create an explicit binary function:\nvar f2 = naryFunction( add, 2 );\n\n// Compute the sum of absolute values:\nvar out = mapReduceRight( x, 0, f1, f2 );\n\nconsole.log( 'x:' );\nconsole.log( x.data );\n\nconsole.log( 'sum: %d', out );\n```\n\n\u003c/section\u003e\n\n\u003c!-- /.examples --\u003e\n\n\u003c!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. --\u003e\n\n\u003csection class=\"references\"\u003e\n\n\u003c/section\u003e\n\n\u003c!-- /.references --\u003e\n\n\u003c!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. --\u003e\n\n\u003csection class=\"related\"\u003e\n\n* * *\n\n## See Also\n\n-   \u003cspan class=\"package-name\"\u003e[`@stdlib/utils-map-right`][@stdlib/utils/map-right]\u003c/span\u003e\u003cspan class=\"delimiter\"\u003e: \u003c/span\u003e\u003cspan class=\"description\"\u003eapply a function to each element in an array and assign the result to an element in an output array, iterating from right to left.\u003c/span\u003e\n-   \u003cspan class=\"package-name\"\u003e[`@stdlib/utils-map-reduce`][@stdlib/utils/map-reduce]\u003c/span\u003e\u003cspan class=\"delimiter\"\u003e: \u003c/span\u003e\u003cspan class=\"description\"\u003eperform a single-pass map-reduce operation against each element in an array and return the accumulated result.\u003c/span\u003e\n-   \u003cspan class=\"package-name\"\u003e[`@stdlib/utils-reduce-right`][@stdlib/utils/reduce-right]\u003c/span\u003e\u003cspan class=\"delimiter\"\u003e: \u003c/span\u003e\u003cspan class=\"description\"\u003eapply a function against an accumulator and each element in an array while iterating from right to left and return the accumulated result.\u003c/span\u003e\n\n\u003c/section\u003e\n\n\u003c!-- /.related --\u003e\n\n\u003c!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. --\u003e\n\n\n\u003csection class=\"main-repo\" \u003e\n\n* * *\n\n## Notice\n\nThis 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.\n\nFor 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].\n\n#### Community\n\n[![Chat][chat-image]][chat-url]\n\n---\n\n## License\n\nSee [LICENSE][stdlib-license].\n\n\n## Copyright\n\nCopyright \u0026copy; 2016-2025. The Stdlib [Authors][stdlib-authors].\n\n\u003c/section\u003e\n\n\u003c!-- /.stdlib --\u003e\n\n\u003c!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. --\u003e\n\n\u003csection class=\"links\"\u003e\n\n[npm-image]: http://img.shields.io/npm/v/@stdlib/utils-map-reduce-right.svg\n[npm-url]: https://npmjs.org/package/@stdlib/utils-map-reduce-right\n\n[test-image]: https://github.com/stdlib-js/utils-map-reduce-right/actions/workflows/test.yml/badge.svg?branch=main\n[test-url]: https://github.com/stdlib-js/utils-map-reduce-right/actions/workflows/test.yml?query=branch:main\n\n[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/utils-map-reduce-right/main.svg\n[coverage-url]: https://codecov.io/github/stdlib-js/utils-map-reduce-right?branch=main\n\n\u003c!--\n\n[dependencies-image]: https://img.shields.io/david/stdlib-js/utils-map-reduce-right.svg\n[dependencies-url]: https://david-dm.org/stdlib-js/utils-map-reduce-right/main\n\n--\u003e\n\n[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg\n[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im\n\n[stdlib]: https://github.com/stdlib-js/stdlib\n\n[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors\n\n[umd]: https://github.com/umdjs/umd\n[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules\n\n[deno-url]: https://github.com/stdlib-js/utils-map-reduce-right/tree/deno\n[deno-readme]: https://github.com/stdlib-js/utils-map-reduce-right/blob/deno/README.md\n[umd-url]: https://github.com/stdlib-js/utils-map-reduce-right/tree/umd\n[umd-readme]: https://github.com/stdlib-js/utils-map-reduce-right/blob/umd/README.md\n[esm-url]: https://github.com/stdlib-js/utils-map-reduce-right/tree/esm\n[esm-readme]: https://github.com/stdlib-js/utils-map-reduce-right/blob/esm/README.md\n[branches-url]: https://github.com/stdlib-js/utils-map-reduce-right/blob/main/branches.md\n\n[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/utils-map-reduce-right/main/LICENSE\n\n[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray-ctor\n\n[@stdlib/array/complex64]: https://github.com/stdlib-js/array-complex64\n\n[@stdlib/array/complex128]: https://github.com/stdlib-js/array-complex128\n\n\u003c!-- \u003crelated-links\u003e --\u003e\n\n[@stdlib/utils/map-right]: https://github.com/stdlib-js/utils-map-right\n\n[@stdlib/utils/map-reduce]: https://github.com/stdlib-js/utils-map-reduce\n\n[@stdlib/utils/reduce-right]: https://github.com/stdlib-js/utils-reduce-right\n\n\u003c!-- \u003c/related-links\u003e --\u003e\n\n\u003c/section\u003e\n\n\u003c!-- /.links --\u003e\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fstdlib-js%2Futils-map-reduce-right","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fstdlib-js%2Futils-map-reduce-right","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fstdlib-js%2Futils-map-reduce-right/lists"}