examples/src/main/python/ml/als_example.py

#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
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# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
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from pyspark.sql import SparkSession

# $example on$
from pyspark.ml.evaluation import RegressionEvaluator
from pyspark.ml.recommendation import ALS
from pyspark.sql import Row
# $example off$

if __name__ == "__main__":
    spark = SparkSession\
        .builder\
        .appName("ALSExample")\
        .getOrCreate()

    # $example on$
    lines = spark.read.text("data/mllib/als/sample_movielens_ratings.txt").rdd
    parts = lines.map(lambda row: row.value.split("::"))
    ratingsRDD = parts.map(lambda p: Row(userId=int(p[0]), movieId=int(p[1]),
                                         rating=float(p[2]), timestamp=int(p[3])))
    ratings = spark.createDataFrame(ratingsRDD)
    (training, test) = ratings.randomSplit([0.8, 0.2])

    # Build the recommendation model using ALS on the training data
    # Note we set cold start strategy to 'drop' to ensure we don't get NaN evaluation metrics
    als = ALS(maxIter=5, regParam=0.01, userCol="userId", itemCol="movieId", ratingCol="rating",
              coldStartStrategy="drop")
    model = als.fit(training)

    # Evaluate the model by computing the RMSE on the test data
    predictions = model.transform(test)
    evaluator = RegressionEvaluator(metricName="rmse", labelCol="rating",
                                    predictionCol="prediction")
    rmse = evaluator.evaluate(predictions)
    print("Root-mean-square error = " + str(rmse))

    # Generate top 10 movie recommendations for each user
    userRecs = model.recommendForAllUsers(10)
    # Generate top 10 user recommendations for each movie
    movieRecs = model.recommendForAllItems(10)

    # Generate top 10 movie recommendations for a specified set of users
    users = ratings.select(als.getUserCol()).distinct().limit(3)
    userSubsetRecs = model.recommendForUserSubset(users, 10)
    # Generate top 10 user recommendations for a specified set of movies
    movies = ratings.select(als.getItemCol()).distinct().limit(3)
    movieSubSetRecs = model.recommendForItemSubset(movies, 10)
    # $example off$
    userRecs.show()
    movieRecs.show()
    userSubsetRecs.show()
    movieSubSetRecs.show()

    spark.stop()