ch3.py 文件源码

def similarity(user_id_a,user_id_b,sim_type=0):
    user_a_tuple_list = userdict[user_id_a].get_items()
    user_b_tuple_list = userdict[user_id_b].get_items()
    common_items=0
    sim = 0.0
    for t1 in user_a_tuple_list:
        for t2 in user_b_tuple_list:
            if (t1[0] == t2[0]):
                common_items += 1
                sim += math.pow(t1[1]-t2[1],2)
    if common_items>0:
        sim = math.sqrt(sim/common_items)
        sim = 1.0 - math.tanh(sim)
        if sim_type==1:
            max_common = min(len(user_a_tuple_list),len(user_b_tuple_list))
            sim = sim * common_items / max_common
    print "User Similarity between",names[user_id_a],"and",names[user_id_b],"is", sim
    return sim #If no common items, returns zero

#3.1
# load movielens data