Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/15484#discussion_r84012469
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala
---
@@ -518,59 +517,64 @@ case class Window(
object Expand {
/**
- * Extract attribute set according to the grouping id.
+ * Build bit mask from attributes of selected grouping set.
*
- * @param bitmask bitmask to represent the selected of the attribute
sequence
- * @param attrs the attributes in sequence
- * @return the attributes of non selected specified via bitmask (with
the bit set to 1)
+ * @param groupingSetAttrs The attributes of selected grouping set
+ * @param attrMap Mapping group by attributes to its index in attributes
sequence
+ * @return The bitmask which represents the selected attributes out of
group by attributes.
+ * A bit in the bitmask is corresponding to an attribute in
group by attributes sequence,
+ * the selected attribute has corresponding bit set to 0 and
otherwise set to 1.
*/
- private def buildNonSelectAttrSet(
- bitmask: Int,
- attrs: Seq[Attribute]): AttributeSet = {
- val nonSelect = new ArrayBuffer[Attribute]()
-
- var bit = attrs.length - 1
- while (bit >= 0) {
- if (((bitmask >> bit) & 1) == 1) nonSelect += attrs(attrs.length -
bit - 1)
- bit -= 1
+ private def buildBitmask(
+ groupingSetAttrs: Seq[Attribute],
+ attrMap: Map[Attribute, Int]): Int = {
+ val numAttributes = attrMap.size
+ val mask = (1 << numAttributes) - 1
+
+ groupingSetAttrs.foldLeft(mask) {
--- End diff --
You only need fold left when you want to traverse the collection in a
certain order. Folds are typically not the easiest to understand, so use them
sparingly and prefer to use more imperative constructs.
Could you rewrite this using a more imperative approach?
Just for kicks & giggles:
```scala
groupingSetAttrs.map(attrMap).map(index => ~(1 << (numAttributes - 1 -
index))).reduce(_ && _)
```
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