Github user feynmanliang commented on a diff in the pull request:
https://github.com/apache/spark/pull/7258#discussion_r34405371
--- Diff:
mllib/src/main/scala/org/apache/spark/mllib/fpm/LocalPrefixSpan.scala ---
@@ -0,0 +1,129 @@
+/*
+ * 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.fpm
+
+import org.apache.spark.Logging
+import org.apache.spark.annotation.Experimental
+
+/**
+ *
+ * :: Experimental ::
+ *
+ * Calculate all patterns of a projected database in local.
+ */
+@Experimental
+private[fpm] object LocalPrefixSpan extends Logging with Serializable {
+
+ /**
+ * Calculate all patterns of a projected database in local.
+ * @param minCount minimum count
+ * @param maxPatternLength maximum pattern length
+ * @param prefix prefix
+ * @param projectedDatabase the projected dabase
+ * @return a set of sequential pattern pairs,
+ * the key of pair is pattern (a list of elements),
+ * the value of pair is the pattern's count.
+ */
+ def run(
+ minCount: Long,
+ maxPatternLength: Int,
+ prefix: Array[Int],
+ projectedDatabase: Array[Array[Int]]): Array[(Array[Int], Long)] = {
+ getPatternsWithPrefix(minCount, maxPatternLength, prefix,
projectedDatabase)
+ }
+
+ /**
+ * calculate suffix sequence following a prefix in a sequence
+ * @param prefix prefix
+ * @param sequence sequence
+ * @return suffix sequence
+ */
+ def getSuffix(prefix: Int, sequence: Array[Int]): Array[Int] = {
+ val index = sequence.indexOf(prefix)
+ if (index == -1) {
+ Array()
+ } else {
+ sequence.drop(index + 1)
+ }
+ }
+
+ /**
+ * Generates frequent items by filtering the input data using minimal
count level.
+ * @param minCount the absolute minimum count
+ * @param sequences sequences data
+ * @return array of item and count pair
+ */
+ private def getFreqItemAndCounts(
+ minCount: Long,
+ sequences: Array[Array[Int]]): Array[(Int, Long)] = {
+ sequences.flatMap(_.distinct)
+ .groupBy(x => x)
+ .mapValues(_.length.toLong)
+ .filter(_._2 >= minCount)
+ .toArray
+ }
+
+ /**
+ * Get the frequent prefixes' projected database.
+ * @param prePrefix the frequent prefixes' prefix
+ * @param frequentPrefixes frequent prefixes
+ * @param sequences sequences data
+ * @return prefixes and projected database
+ */
+ private def getPatternAndProjectedDatabase(
+ prePrefix: Array[Int],
+ frequentPrefixes: Array[Int],
+ sequences: Array[Array[Int]]): Array[(Array[Int],
Array[Array[Int]])] = {
+ val filteredProjectedDatabase = sequences
+ .map(x => x.filter(frequentPrefixes.contains(_)))
+ frequentPrefixes.map { x =>
+ val sub = filteredProjectedDatabase.map(y => getSuffix(x,
y)).filter(_.nonEmpty)
+ (prePrefix ++ Array(x), sub)
+ }.filter(x => x._2.nonEmpty)
+ }
+
+ /**
+ * Calculate all patterns of a projected database in local.
--- End diff --
No need for "in local" since object's name makes this clear
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