[SPARK-10028][MLLIB][PYTHON] Add Python API for PrefixSpan

Author: Yu ISHIKAWA <yuu.ishikawa@gmail.com>

Closes #9469 from yu-iskw/SPARK-10028.

mllib/src/main/scala/org/apache/spark/mllib/api/python/PrefixSpanModelWrapper.scala

@@ -0,0 +1,32 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * 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
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.mllib.api.python
+
+import org.apache.spark.mllib.fpm.PrefixSpanModel
+import org.apache.spark.rdd.RDD
+
+/**
+ * A Wrapper of PrefixSpanModel to provide helper method for Python
+ */
+private[python] class PrefixSpanModelWrapper(model: PrefixSpanModel[Any])
+  extends PrefixSpanModel(model.freqSequences) {
+
+  def getFreqSequences: RDD[Array[Any]] = {
+    SerDe.fromTuple2RDD(model.freqSequences.map(x => (x.javaSequence, x.freq)))
+  }
+}

mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala

@@ -35,7 +35,7 @@ import org.apache.spark.mllib.classification._
 import org.apache.spark.mllib.clustering._
 import org.apache.spark.mllib.evaluation.RankingMetrics
 import org.apache.spark.mllib.feature._
-import org.apache.spark.mllib.fpm.{FPGrowth, FPGrowthModel}
+import org.apache.spark.mllib.fpm.{FPGrowth, FPGrowthModel, PrefixSpan}
 import org.apache.spark.mllib.linalg._
 import org.apache.spark.mllib.linalg.distributed._
 import org.apache.spark.mllib.optimization._
@@ -557,6 +557,27 @@ private[python] class PythonMLLibAPI extends Serializable {
     new FPGrowthModelWrapper(model)
   }
 
+  /**
+   * Java stub for Python mllib PrefixSpan.train().  This stub returns a handle
+   * to the Java object instead of the content of the Java object.  Extra care
+   * needs to be taken in the Python code to ensure it gets freed on exit; see
+   * the Py4J documentation.
+   */
+  def trainPrefixSpanModel(
+      data: JavaRDD[java.util.ArrayList[java.util.ArrayList[Any]]],
+      minSupport: Double,
+      maxPatternLength: Int,
+      localProjDBSize: Int ): PrefixSpanModelWrapper = {
+    val prefixSpan = new PrefixSpan()
+      .setMinSupport(minSupport)
+      .setMaxPatternLength(maxPatternLength)
+      .setMaxLocalProjDBSize(localProjDBSize)
+
+    val trainData = data.rdd.map(_.asScala.toArray.map(_.asScala.toArray))
+    val model = prefixSpan.run(trainData)
+    new PrefixSpanModelWrapper(model)
+  }
+
   /**
    * Java stub for Normalizer.transform()
    */

python/pyspark/mllib/fpm.py

@@ -23,7 +23,7 @@ from pyspark import SparkContext, since
 from pyspark.rdd import ignore_unicode_prefix
 from pyspark.mllib.common import JavaModelWrapper, callMLlibFunc, inherit_doc
 
-__all__ = ['FPGrowth', 'FPGrowthModel']
+__all__ = ['FPGrowth', 'FPGrowthModel', 'PrefixSpan', 'PrefixSpanModel']
 
 
 @inherit_doc
@@ -85,6 +85,73 @@ class FPGrowth(object):
         """
 
 
+@inherit_doc
+@ignore_unicode_prefix
+class PrefixSpanModel(JavaModelWrapper):
+    """
+    .. note:: Experimental
+
+    Model fitted by PrefixSpan
+
+    >>> data = [
+    ...    [["a", "b"], ["c"]],
+    ...    [["a"], ["c", "b"], ["a", "b"]],
+    ...    [["a", "b"], ["e"]],
+    ...    [["f"]]]
+    >>> rdd = sc.parallelize(data, 2)
+    >>> model = PrefixSpan.train(rdd)
+    >>> sorted(model.freqSequences().collect())
+    [FreqSequence(sequence=[[u'a']], freq=3), FreqSequence(sequence=[[u'a'], [u'a']], freq=1), ...
+
+    .. versionadded:: 1.6.0
+    """
+
+    @since("1.6.0")
+    def freqSequences(self):
+        """Gets frequence sequences"""
+        return self.call("getFreqSequences").map(lambda x: PrefixSpan.FreqSequence(x[0], x[1]))
+
+
+class PrefixSpan(object):
+    """
+    .. note:: Experimental
+
+    A parallel PrefixSpan algorithm to mine frequent sequential patterns.
+    The PrefixSpan algorithm is described in J. Pei, et al., PrefixSpan:
+    Mining Sequential Patterns Efficiently by Prefix-Projected Pattern Growth
+    ([[http://doi.org/10.1109/ICDE.2001.914830]]).
+
+    .. versionadded:: 1.6.0
+    """
+
+    @classmethod
+    @since("1.6.0")
+    def train(cls, data, minSupport=0.1, maxPatternLength=10, maxLocalProjDBSize=32000000):
+        """
+        Finds the complete set of frequent sequential patterns in the input sequences of itemsets.
+
+        :param data: The input data set, each element contains a sequnce of itemsets.
+        :param minSupport: the minimal support level of the sequential pattern, any pattern appears
+            more than  (minSupport * size-of-the-dataset) times will be output (default: `0.1`)
+        :param maxPatternLength: the maximal length of the sequential pattern, any pattern appears
+            less than maxPatternLength will be output. (default: `10`)
+        :param maxLocalProjDBSize: The maximum number of items (including delimiters used in
+            the internal storage format) allowed in a projected database before local
+            processing. If a projected database exceeds this size, another
+            iteration of distributed prefix growth is run. (default: `32000000`)
+        """
+        model = callMLlibFunc("trainPrefixSpanModel",
+                              data, minSupport, maxPatternLength, maxLocalProjDBSize)
+        return PrefixSpanModel(model)
+
+    class FreqSequence(namedtuple("FreqSequence", ["sequence", "freq"])):
+        """
+        Represents a (sequence, freq) tuple.
+
+        .. versionadded:: 1.6.0
+        """
+
+
 def _test():
     import doctest
     import pyspark.mllib.fpm