examples/src/main/python/mllib/dataset_example.py

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"""
An example of how to use DataFrame as a dataset for ML. Run with::
    bin/spark-submit examples/src/main/python/mllib/dataset_example.py
"""
from __future__ import print_function

import os
import sys
import tempfile
import shutil

from pyspark import SparkContext
from pyspark.sql import SQLContext
from pyspark.mllib.util import MLUtils
from pyspark.mllib.stat import Statistics


def summarize(dataset):
    print("schema: %s" % dataset.schema().json())
    labels = dataset.map(lambda r: r.label)
    print("label average: %f" % labels.mean())
    features = dataset.map(lambda r: r.features)
    summary = Statistics.colStats(features)
    print("features average: %r" % summary.mean())

if __name__ == "__main__":
    if len(sys.argv) > 2:
        print("Usage: dataset_example.py <libsvm file>", file=sys.stderr)
        exit(-1)
    sc = SparkContext(appName="DatasetExample")
    sqlContext = SQLContext(sc)
    if len(sys.argv) == 2:
        input = sys.argv[1]
    else:
        input = "data/mllib/sample_libsvm_data.txt"
    points = MLUtils.loadLibSVMFile(sc, input)
    dataset0 = sqlContext.inferSchema(points).setName("dataset0").cache()
    summarize(dataset0)
    tempdir = tempfile.NamedTemporaryFile(delete=False).name
    os.unlink(tempdir)
    print("Save dataset as a Parquet file to %s." % tempdir)
    dataset0.saveAsParquetFile(tempdir)
    print("Load it back and summarize it again.")
    dataset1 = sqlContext.parquetFile(tempdir).setName("dataset1").cache()
    summarize(dataset1)
    shutil.rmtree(tempdir)