共通友達を数えるMrJob

friends.list

W, A, B, C
X, A, B, C, D, Z
Y, A, B, E
Z, A, B, D, E

recommendation.py

from mrjob.job import MRJob

class Recommendation(MRJob):
    def mapper(self, key, line):
        input = line.split(',')
        user, friends = input[0], input[1:]
        for i in range(len(friends)):
            f1 = friends[i].strip()
            for j in range(i+1, len(friends)):
                f2 = friends[j].strip()
                if f1 < f2:
                    yield(f1, f2), 1
                else:
                    yield(f2, f1), 1

    def reducer(self, key, values):
        f1, f2 = key
        mutual_friends_count = 0
        for value in values:
            mutual_friends_count += value

        yield (f1, f2), mutual_friends_count

if __name__ == '__main__':
    Recommendation.run()