srowen commented on a change in pull request #28206: [SPARK-31436][ML] MinHash
keyDistance optimization
URL: https://github.com/apache/spark/pull/28206#discussion_r407510019
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File path: mllib/src/main/scala/org/apache/spark/ml/feature/MinHashLSH.scala
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@@ -70,19 +70,51 @@ class MinHashLSHModel private[ml](
@Since("2.1.0")
override protected[ml] def keyDistance(x: Vector, y: Vector): Double = {
- val xSet = x.nonZeroIterator.map(_._1).toSet
- val ySet = y.nonZeroIterator.map(_._1).toSet
- val intersectionSize = xSet.intersect(ySet).size.toDouble
- val unionSize = xSet.size + ySet.size - intersectionSize
+ val xIter = x.nonZeroIterator.map(_._1)
+ val yIter = y.nonZeroIterator.map(_._1)
+ if (xIter.isEmpty) {
+ assert(yIter.hasNext, "The union of two input sets must have at least 1
elements")
+ return 1.0
+ } else if (yIter.isEmpty) {
+ return 1.0
+ }
+
+ var xIndex = xIter.next
+ var yIndex = yIter.next
+ var xSize = 1
+ var ySize = 1
+ var intersectionSize = 0
+
+ while (xIndex != -1 || yIndex != -1) {
+ if (xIndex != -1 && yIndex != -1) {
+ if (xIndex == yIndex) {
+ intersectionSize += 1
+ xIndex = if (xIter.hasNext) { xSize += 1; xIter.next } else -1
+ yIndex = if (yIter.hasNext) { ySize += 1; yIter.next } else -1
+ } else if (xIndex > yIndex) {
+ yIndex = if (yIter.hasNext) { ySize += 1; yIter.next } else -1
+ } else {
+ xIndex = if (xIter.hasNext) { xSize += 1; xIter.next } else -1
+ }
+ } else if (xIndex != -1) {
+ while (xIter.hasNext) { xIndex = xIter.next; xSize += 1 }
Review comment:
Do you need to update xIndex in this case, and yIndex below? looks like
you're just counting the remaining size of the iterator. It's possible .size()
is as fast from here.
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