Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/23048#discussion_r234399421
--- Diff:
mllib-local/src/main/scala/org/apache/spark/ml/linalg/Vectors.scala ---
@@ -370,14 +370,19 @@ object Vectors {
case (v1: DenseVector, v2: SparseVector) =>
squaredDistance = sqdist(v2, v1)
- case (DenseVector(vv1), DenseVector(vv2)) =>
- var kv = 0
+ case (DenseVector(vv1), DenseVector(vv2)) => {
val sz = vv1.length
- while (kv < sz) {
- val score = vv1(kv) - vv2(kv)
- squaredDistance += score * score
- kv += 1
+ @annotation.tailrec
--- End diff --
FWIW, I did an experimental by myself before because someone proposed
similar change (turning `while` to tail recursive one). There was no virtual
difference. If this change is only tail recursion vs `while`, I doubt how much
it can improve. I believe the benchmark steps should be clarified.
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