Collaborative Filtering ALS Recommender System using Spark MLlib adapted from the Spark Summit 2014 Recommender System training example

## recommender_spark.py
#!/usr/bin/env python

import sys
import itertools
from math import sqrt
from operator import add
from os.path import join, isfile, dirname
from time import time

from pyspark import SparkConf, SparkContext
from pyspark.mllib.recommendation import ALS

def parseRating(line):
    """
    Parses a rating record in MovieLens format userId[tab]movieId[tab]rating[tab]timestamp .
    """
    fields = line.strip().split("\t")
    return long(fields[3]) % 10, (int(fields[0]), int(fields[1]), float(fields[2]))

def loadRatings(ratingsFile):
    """
    Load ratings from file.
    """
    if not isfile(ratingsFile):
        print "File %s does not exist." % ratingsFile
        sys.exit(1)
    f = open(ratingsFile, 'r')
    ratings = filter(lambda r: r[2] > 0, [parseRating(line)[1] for line in f])
    f.close()
    if not ratings:
        print "No ratings provided."
        sys.exit(1)
    else:
        return ratings

def computeRmse(model, data, n):
    """
    Compute RMSE (Root Mean Squared Error).
    """
    predictions = model.predictAll(data.map(lambda x: (x[0], x[1])))
    predictionsAndRatings = predictions.map(lambda x: ((x[0], x[1]), x[2])) \
      .join(data.map(lambda x: ((x[0], x[1]), x[2]))) \
      .values()
    return sqrt(predictionsAndRatings.map(lambda x: (x[0] - x[1]) ** 2).reduce(add) / float(n))


def main():

    if (len(sys.argv) != 2):
        print "Usage: /path/to/spark/bin/spark-submit --driver-memory 2g " + \
          "python-file-name.py /path/to/training-data-file"
        sys.exit(1)

    startTime = time()

    conf = SparkConf().setMaster("local").setAppName("movieRecommender").set("spark.executor.memory", "2g")
    sc = SparkContext(conf=conf)

    # ratings is an RDD of (last digit of timestamp, (userId, movieId, rating))
    trainingDataFile = sys.argv[1]
    ratings = sc.textFile(trainingDataFile).map(parseRating)

    numRatings = ratings.count()
    numUsers = ratings.values().map(lambda r: r[0]).distinct().count()
    numMovies = ratings.values().map(lambda r: r[1]).distinct().count()

    print "Got %d ratings from %d users on %d movies." % (numRatings, numUsers, numMovies)

    numPartitions = 4
    training = ratings.filter(lambda x: x[0] < 6) \
      .values() \
      .repartition(numPartitions) \
      .cache()

    validation = ratings.filter(lambda x: x[0] >= 6 and x[0] < 8) \
      .values() \
      .repartition(numPartitions) \
      .cache()

    test = ratings.filter(lambda x: x[0] >= 8).values().cache()

    numTraining = training.count()
    numValidation = validation.count()
    numTest = test.count()

    print "Training: %d, validation: %d, test: %d" % (numTraining, numValidation, numTest)

    ranks = [6, 8, 12]
    lambdas = [0.1, 1.0, 10.0]
    numIters = [10, 20]
    bestModel = None
    bestValidationRmse = float("inf")
    bestRank = 0
    bestLambda = -1.0
    bestNumIter = -1

    for rank, lmbda, numIter in itertools.product(ranks, lambdas, numIters):
        model = ALS.train(training, rank, numIter, lmbda)
        validationRmse = computeRmse(model, validation, numValidation)
        print "RMSE (validation) = %f for the model trained with " % validationRmse + \
              "rank = %d, lambda = %.1f, and numIter = %d." % (rank, lmbda, numIter)
        if (validationRmse < bestValidationRmse):
            bestModel = model
            bestValidationRmse = validationRmse
            bestRank = rank
            bestLambda = lmbda
            bestNumIter = numIter

    # evaluate the best model on the test set
    testRmse = computeRmse(bestModel, test, numTest)


    sc.stop()
    endTime = time()
    programTime = endTime - startTime

    print "Got %d ratings from %d users on %d movies." % (numRatings, numUsers, numMovies)
    print "Training: %d, validation: %d, test: %d" % (numTraining, numValidation, numTest)
    print "The best model was trained with rank = %d and lambda = %.1f, " % (bestRank, bestLambda) \
      + "and numIter = %d, and its RMSE on the test set is %f." % (bestNumIter, testRmse)
    print "Time for program to complete: %.1f s" %programTime

if __name__ == "__main__":
    main()