Github user hhbyyh commented on a diff in the pull request:
https://github.com/apache/spark/pull/6538#discussion_r31490778
--- Diff: mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala ---
@@ -82,6 +82,19 @@ object MLUtils {
val value = indexAndValue(1).toDouble
(index, value)
}.unzip
+
+ // check if indices is one-based and in ascending order
--- End diff --
There seems to be some performance difference.
```
val indices = 1 to 200000000
var start = System.nanoTime()
var previous = -1
var i = 0
val indicesLength = indices.size
while (i < indicesLength) {
if (indices(i) <= previous) {
throw new IllegalArgumentException("indices should be one-based and
in ascending order")
}
previous = indices(i)
i += 1
}
println("while: " + (System.nanoTime() - start).toDouble / 1e9)
start = System.nanoTime()
val g = indices.sliding(2).forall(p => p(0) < p(1))
println("sliding: " + (System.nanoTime() - start).toDouble / 1e9)
```
while: 0.088418226
sliding: 37.128311352
I also used jconsole to collect the memory usage. The "sliding" way
consumes significantly higher memory and triggers GC frequently/
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