Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/7818#discussion_r36024394
--- Diff: mllib/src/main/scala/org/apache/spark/mllib/fpm/PrefixSpan.scala
---
@@ -237,13 +247,33 @@ class PrefixSpan private (
*/
private def getPatternsInLocal(
minCount: Long,
- data: RDD[(List[Int], Iterable[Array[Int]])]): RDD[(List[Int],
Long)] = {
+ data: RDD[(List[Set[Int]], Iterable[List[Set[Int]]])]):
RDD[(List[Set[Int]], Long)] = {
data.flatMap {
- case (prefix, projDB) =>
- LocalPrefixSpan.run(minCount, maxPatternLength,
prefix.toList.reverse, projDB)
- .map { case (pattern: List[Int], count: Long) =>
- (pattern.reverse, count)
- }
+ case (prefix, projDB) => LocalPrefixSpan.run(minCount,
maxPatternLength, prefix, projDB)
+ }
+ }
+
+}
+
+object PrefixSpan {
+ private[fpm] val DELIMITER = -1
+
+ private[fpm] def splitAtDelimiter(pattern: List[Int]): List[Set[Int]] = {
+ pattern.span(_ != DELIMITER) match {
+ case (x, xs) if xs.length > 1 => x.toSet :: splitAtDelimiter(xs.tail)
+ case (x, xs) => List(x.toSet)
}
}
+
+ private[fpm] def insertDelimiters(sequence: List[Set[Int]]): List[Int] =
{
+ // TODO: avoid allocating new arrays when appending
+ sequence.zip(Seq.fill(sequence.size)(PrefixSpan.DELIMITER))
--- End diff --
Use `ArrayBuilder` instead of functional style. Creating a sequence of
delimiters is not efficient. As a reference, Scala also use builder in
`mkString`:
https://github.com/scala/scala/blob/2.11.x/src/library/scala/collection/TraversableOnce.scala#L351.
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