• first class functions
• higher order functions
• purity
• immutability
• composition
• partial application & curry
• recursion & optimization
• Lazy evaluation

Reduce

Map

Filter

Ramda is NOT a drop-in replacement for Underscore (or LoDash). It is intended to work with a different style of coding.

Underscore/LoDash
_.map([1, 2, 3], multiply3);
// → [3, 6, 9]

Ramda
R.map(multiply3, [1, 2, 3]);

// → [3, 6, 9]

Currying is the process of turning a function that expects multiple parameters into one that, when supplied fewer parameters, returns a new function that awaits the remaining ones.

var getProperty = R.curry(function(prop, obj) {
    return obj[prop];
});

var getProperty = function(prop, obj) {
    return obj[prop];
};


var name = getProperty('name', {'name' : 'damillionaire'});

var getName = getProperty('name');

var double = R.multiply(2);

double(13);  // → 26

var greater = function(a,b) {
  return a > b ? a : b;
};

var max = R.reduce(greater, -Infinity);

max([1,-3483,9,7,2]) // 9
max([-21,-3483,-2,-1]) // -1

R.multiply(2, 13); // → 26

underscore/lodash

var firstTwoLetters = function(words) {
  return _.map(words, function(word) {
    return _.first(word, 2);
  });
}

firstTwoLetters(['andy', 'nero']); 
// [‘an’, ‘ne’]

Ramda.js

var firstTwoLetters = R.map(R.first(2));

firstTwoLetters(['andy', 'nero']); 
// [‘an’, ‘ne’]

function compose(g, f) {
  return function(x) {
    return g(f(x));
  };
}

var wordCount = R.compose(R.length, R.split(' '));

wordCount("There are seven words in this sentence"); // 7

var wordCount = function(str) {
    var words = _.split(' ', str);
        return _.length(words);
}

wordCount("There are seven words in this sentence"); // 7

"Cool. But does it do promises?"

var data = {
    result: "SUCCESS",
    interfaceVersion: "1.0.3",
    requested: "10/17/2013 15:31:20",
    lastUpdated: "10/16/2013 10:52:39",
    tasks: [
        {id: 104, complete: false,            priority: "high",
                  dueDate: "2013-11-29",      username: "Scott",
                  title: "Do something",      created: "9/22/2013"},
        {id: 105, complete: false,            priority: "medium",
                  dueDate: "2013-11-22",      username: "Lena",
                  title: "Do something else", created: "9/22/2013"},
        {id: 107, complete: true,             priority: "high",
                  dueDate: "2013-11-22",      username: "Mike",
                  title: "Fix the foo",       created: "9/22/2013"},
        {id: 108, complete: false,            priority: "low",
                  dueDate: "2013-11-15",      username: "Punam",
                  title: "Adjust the bar",    created: "9/25/2013"},
        {id: 110, complete: false,            priority: "medium",
                  dueDate: "2013-11-15",      username: "Scott",
                  title: "Rename everything", created: "10/2/2013"},
        {id: 112, complete: true,             priority: "high",
                  dueDate: "2013-11-27",      username: "Lena",
                  title: "Alter all quuxes",  created: "10/5/2013"}
        // , ...
    ]
};

getIncompleteTaskSummaries("Scott").then(log, log);




// OUTPUT
[
    {id: 110, title: "Rename everything", 
        dueDate: "2013-11-15", priority: "medium"},
    {id: 104, title: "Do something", 
        dueDate: "2013-11-29", priority: "high"}
]

function log(x) {
    console.log(x);
    return x;
};


var getIncompleteTaskSummaries = 

R.pCompose(sortByDueDate,
           getRequiredFields,
           removeStatusComplete) 
           log,
           filterUsername,
           getTasks,
           log,
           fetchData);


getIncompleteTaskSummaries("Scott").then(log, log)

"R.map(parseInt, ['10', '10', '10']);"
[10, 10, 10]

map, reduce, filter 

+ Functor's

=

var setResults = setHtml('#results');

var renderVideos = R.map(render);

var getVideos = R.pCompose(R.prop('entry'),
                          R.prop('feed'),     
                          R.prop('data'));

var queryYoutube = R.pCompose(setResults, 
                              renderVideos, 
                              getVideos, 
                              http.getJSON);

queryYoutube(query).then(log, log);