eatoncys edited a comment on issue #24238: [SPARK-27320][SQL]Converting seq to array in AggregationIterator to improve its access performance URL: https://github.com/apache/spark/pull/24238#issuecomment-477837590 @HyukjinKwon, I constructed a test case that used `for` and `index` to access a list which hive 1000 elements, the result is like below, `calculateWithFor` is 6x faster than `calculateWithIndex` calculateWithIndex cost: 6813710 ns calculateWithFor cost: 1257866 ns ``` def calculateWithFor(in: Seq[Int]): Array[Int] = { val result = new Array[Int](in.length) var i: Int = 0 for (x <- in) { result(i) = x i = i + 1 } result } def calculateWithIndex(in: Seq[Int]): Array[Int] = { val result = new Array[Int](in.length) val length = in.length var i: Int = 0 while(i < length) { result(i) = in(i) i = i + 1 } result } ```
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