Github user ericl commented on a diff in the pull request:
https://github.com/apache/spark/pull/13505#discussion_r65821238
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/package.scala
---
@@ -86,11 +88,42 @@ package object expressions {
/**
* Helper functions for working with `Seq[Attribute]`.
*/
- implicit class AttributeSeq(attrs: Seq[Attribute]) {
+ implicit class AttributeSeq(val attrs: Seq[Attribute]) {
/** Creates a StructType with a schema matching this `Seq[Attribute]`.
*/
def toStructType: StructType = {
StructType(attrs.map(a => StructField(a.name, a.dataType,
a.nullable)))
}
+
+ // It's possible that `attrs` is a linked list, which can lead to bad
O(n^2) loops when
+ // accessing attributes by their ordinals. To avoid this performance
penalty, convert the input
+ // to an array.
+ private lazy val attrsArray = attrs.toArray
+
+ private lazy val exprIdToOrdinal = {
+ val arr = attrsArray
+ val map = Maps.newHashMapWithExpectedSize[ExprId, Int](arr.length)
+ var index = 0
+ while (index < arr.length) {
+ val exprId = arr(index).exprId
+ if (!map.containsKey(exprId)) {
+ map.put(exprId, index)
--- End diff --
Is it necessary to check containsKey before the put?
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