srowen commented on a change in pull request #25442: [SPARK-28722][ML] Change
sequential label sorting in StringIndexer fit to parallel
URL: https://github.com/apache/spark/pull/25442#discussion_r313993165
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File path: mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala
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@@ -213,32 +221,36 @@ class StringIndexer @Since("1.4.0") (
val labelsArray = $(stringOrderType) match {
case StringIndexer.frequencyDesc =>
val sortFunc = StringIndexer.getSortFunc(ascending = false)
- countByValue(dataset, inputCols).map { counts =>
+ val orgStrings = countByValue(dataset, inputCols).toSeq
+ ThreadUtils.parmap(orgStrings, "sortingStringLabels", 8) { counts =>
counts.toSeq.sortWith(sortFunc).map(_._1).toArray
- }
+ }.toArray
case StringIndexer.frequencyAsc =>
Review comment:
PS I wonder if we can reduce the code duplication while we're at it. Each
pair of cases is almost identical. Maybe they can share the handling and just
vary one element (asc/desc) by checking the actual value one more time in the
block
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