Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/15484#discussion_r84001582
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -216,10 +216,16 @@ class Analyzer(
* Group Count: N + 1 (N is the number of group expressions)
*
* We need to get all of its subsets for the rule described above,
the subset is
- * represented as the bit masks.
+ * represented as sequence of expressions.
*/
- def bitmasks(r: Rollup): Seq[Int] = {
- Seq.tabulate(r.groupByExprs.length + 1)(idx => (1 << idx) - 1)
+ def selectGroupExprsRollup(exprs: Seq[Expression]):
Seq[Seq[Expression]] = {
--- End diff --
This is too complex. It is hard to grasp what is going on here. Lets make
this imperative:
```scala
val buffer = mutable.Buffer.empty[Seq[Expression]]
var current = exprs
while (current.nonEmpty) {
buffer += current
current = current.init
}
buffer
```
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