Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/7945#discussion_r36312205
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/stat/FrequentItems.scala
---
@@ -38,13 +37,22 @@ private[sql] object FrequentItems extends Logging {
def add(key: Any, count: Long): this.type = {
if (baseMap.contains(key)) {
baseMap(key) += count
+ if (baseMap(key) < minCount) minCount = baseMap(key)
} else {
if (baseMap.size < size) {
baseMap += key -> count
+ if (count < minCount) minCount = count
} else {
- // TODO: Make this more efficient... A flatMap?
- baseMap.retain((k, v) => v > count)
- baseMap.transform((k, v) => v - count)
+ val remainder = count - minCount
+ if (remainder >= 0) {
+ baseMap += key -> count // something will get kicked out, so
we can add this
+ baseMap.retain((k, v) => v > minCount)
+ baseMap.transform((k, v) => v - minCount)
+ minCount = baseMap.foldLeft(Long.MaxValue)((a, b) =>
math.min(a, b._2))
--- End diff --
Since we still need to recompute `minCount` after each update, I think the
code is simpler without tracking `minCount` in all cases. We can compute
`minCount` directly in this branch.
~~~scala
if (baseMap.contains(key)) {
baseMap(key) += count
} else {
baseMap(key) = count
if (baseMap.size > size) {
val minCount = baseMap.values.min
baseMap.retain((_, v) => v > minCount)
baseMap.transform((_, v) => v - minCount)
}
}
~~~
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