ramda

What is ramda?

Ramda is a functional programming library for JavaScript that makes it easy to create functional pipelines, without mutating data. It emphasizes a purer functional style, with functions that are automatically curried and composed of small, reusable, and combinable functions.

What are ramda's main functionalities?

Immutability and Side-Effect Free Functions

Ramda functions do not mutate the input data and do not cause side effects, making it easier to reason about code.

const increment = R.map(R.add(1));
const result = increment([1, 2, 3]); // [2, 3, 4]

Function Composition

Ramda provides compose and pipe functions for combining functions into new functions, facilitating functional composition.

const getNames = R.compose(R.map(R.prop('name')), R.filter(R.propEq('isActive', true)));
const users = [{name: 'Alice', isActive: true}, {name: 'Bob', isActive: false}];
const activeUserNames = getNames(users); // ['Alice']

Automatic Currying

Ramda functions are automatically curried, allowing you to easily create new functions by partially applying arguments.

const addFourNumbers = (a, b, c, d) => a + b + c + d;
const curriedAddFourNumbers = R.curry(addFourNumbers);
const f = curriedAddFourNumbers(1, 2);
const g = f(3);
const result = g(4); // 10

Data Transformation

Ramda provides a suite of tools for transforming data structures, such as arrays and objects, in a declarative and functional way.

const sortByAge = R.sortBy(R.prop('age'));
const people = [{name: 'John', age: 23}, {name: 'Jane', age: 21}];
const sortedPeople = sortByAge(people); // [{name: 'Jane', age: 21}, {name: 'John', age: 23}]

Other packages similar to ramda

lodash

Lodash is a JavaScript utility library that offers similar functionality to Ramda, such as data manipulation and functional utilities. However, Lodash is not as strictly functional as Ramda and does not emphasize currying and function composition to the same extent.

underscore

Underscore.js is another utility library that provides functional programming helpers. It is similar to Lodash and predates both Lodash and Ramda. It has a more OOP-style approach and lacks the auto-currying and functional composition features that are core to Ramda.

immutable

Immutable.js provides persistent immutable data structures which can be used in a functional programming style. Unlike Ramda, which works with plain JavaScript types, Immutable.js uses its own types and provides different APIs for manipulating these structures.

fp-ts

fp-ts is a library for typed functional programming in TypeScript. It provides type-safe functional programming structures and utilities, and it is more focused on types and type-level programming compared to Ramda.

README

Ramda

A practical functional library for Javascript programmers.


Why Ramda?

There are already several excellent libraries with a functional flavor. Typically, they are meant to be general-purpose toolkits, suitable for working in multiple paradigms. Ramda has a more focused goal. We wanted a library designed specifically for a functional programming style, one that makes it easy to create functional pipelines, one that never mutates user data.

What's Different?

The primary distinguishing features of Ramda are:

• Ramda emphasizes a purer functional style. Immutability and side-effect free functions are at the heart of its design philosophy. This can help you get the job done with simple, elegant code.

• Ramda functions are automatically curried. This allows you to easily build up new functions from old ones simply by not supplying the final parameters.

• The parameters to Ramda functions are arranged to make it convenient for currying. The data to be operated on is generally supplied last.

The last two points together make it very easy to build functions as sequences of simpler functions, each of which transforms the data and passes it along to the next. Ramda is designed to support this style of coding.

Also see Why Ramda?, Why Curry Helps and Hey Underscore, You're Doing It Wrong!.

Philosophy

Using Ramda should feel much like just using Javascript. It is practical, functional Javascript. We're not introducing lambda expressions in strings, we're not borrowing consed lists, we're not porting over all of the Clojure functions.

Our basic data structures are plain Javascript objects, and our usual collections are Javascript arrays. We also keep other native features of Javascript, such as functions as objects with properties.

Functional programming is in good part about immutable objects and side-effect free functions. While Ramda does not enforce this, it enables such style to be as frictionless as possible.

We aim for an implementation both clean and elegant, but the API is king. We sacrifice a great deal of implementation elegance for even a slightly cleaner API.

Last but not least, Ramda strives for performance. A reliable and quick implementation wins over any notions of functional purity.

Installation

To use with node:

$ npm install ramda

Then in the console:

var R = require('ramda');

To use directly in the browser:

<script src="path/to/yourCopyOf/ramda.js"></script>

or the minified version:

<script src="path/to/yourCopyOf/ramda.min.js"></script>

or from a CDN, either cdnjs:

<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.18.0/ramda.min.js"></script>

or one of the below links from jsDelivr:

<script src="//cdn.jsdelivr.net/ramda/0.18.0/ramda.min.js"></script>
<script src="//cdn.jsdelivr.net/ramda/0.18/ramda.min.js"></script>
<script src="//cdn.jsdelivr.net/ramda/latest/ramda.min.js"></script>

(note that using latest is taking a significant risk that ramda API changes could break your code.)

These script tags add the variable R on the browser's global scope.

Or you can inject ramda into virtually any unsuspecting website using the bookmarklet.

Build

• on Unix-based platforms, npm run build updates dist/ramda.js and dist/ramda.min.js
• on Windows, write the output of scripts/build --complete to a temporary file, then rename the temporary file dist/ramda.js.

Partial Builds

It is possible to build Ramda with a subset of the functionality to reduce its file size. Ramda's build system supports this with command line flags. For example if you're using R.compose, R.reduce, and R.filter you can create a partial build with:

./scripts/build -- src/compose.js src/reduce.js src/filter.js > dist/ramda.custom.js

This requires having Node/io.js installed.

Documentation

Please review the API documentation.

Introductions

• Introducing Ramda by Buzz de Cafe
• Why Ramda? by Scott Sauyet
• Favoring Curry by Scott Sauyet

The Name

Ok, so we like sheep. That's all. It's a short name, not already taken. It could as easily have been eweda, but then we would be forced to say eweda lamb!, and no one wants that. For non-English speakers, lambs are baby sheep, ewes are female sheep, and rams are male sheep. So perhaps ramda is a grown-up lambda... but probably not.

Running The Test Suite

Console:

To run the test suite from the console, you need to have mocha installed:

npm install -g mocha

Then from the root of the project, you can just call

mocha

Alternately, if you've installed the dependencies, via:

npm install

then you can run the tests (and get detailed output) by running:

npm test

Browser:

To run the test suite in the browser, you can simply open test/index.html.

Alternatively, you can use testem to test across different browsers (or even headlessly), with livereloading of tests too. Install testem (npm install -g testem) and run testem. Open the link provided in your browser and you will see the results in your terminal.

If you have PhantomJS installed, you can run testem -l phantomjs to run the tests completely headlessly.

Acknowledgements

Thanks to J. C. Phillipps for the Ramda logo. Ramda logo artwork © 2014 J. C. Phillipps. Licensed Creative Commons CC BY-NC-SA 3.0.