rxtweetstream.js

var Rx = require('./rx.node')
,   twitter = require('ntwitter')
,   credentials = require('./credentials')
,   io = require('socket.io').listen(80);

var customBind = function (self, method) {
    return function () {
        return self[method].apply(self, arguments);
    };
};

// Turn twitter into stream
twitter.prototype.streamAsObservable = function (url, data) {
    return Rx.Observable.create(function (observer) {
        var outerStream;
        twit.stream(url, data, function (stream) {
            outerStream = stream;

            // Handle events
            var onCompleted = customBind(observer, 'onCompleted');
            stream.on('data', customBind(observer, 'onNext'));
            stream.on('end', onCompleted);
            stream.on('destroy', onCompleted);
            stream.on('error', customBind(observer, 'onError'));
        });

        // Destroy upon exiting
        return function () {
            if (outerStream) {
                outerStream.destroy();
            }
        };
    });
};

var twit = new twitter(credentials);

var tweetStream = twit.streamAsObservable('statuses/sample');

// Group by language of the user
var groupedTweetStream = tweetStream.groupBy(function (tweet) { 
	return tweet.user.lang;
});

io.sockets.on('connection', function (socket) {

    // Get grouping
	groupedTweetStream.subscribe(function (groupedTweet) {

        // Aggregate tweet count based upon language
		groupedTweet.scan({count: 0, key: groupedTweet.key }, function (acc, x) {
			return { key: groupedTweet.key, count: acc.count + 1, text: x.text };
        }).subscribe(function (status) {

            // Emit data
		    io.sockets.emit('message', {
		        languageCode: status.key,
		        tweetCount: status.count,
		        text: status.text
		    });
		});
	}, function (err) {
	    io.sockets.emit('error', err);
	});
});

Very nice!