felixcheung 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_r313712444
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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 =>
Review comment:
how is 8 picked here? should this be ~= number of driver core or something?
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