maropu commented on a change in pull request #32498:
URL: https://github.com/apache/spark/pull/32498#discussion_r631548474
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala
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@@ -789,6 +797,38 @@ case class Range(
}
}
+ private def computeHistogramStatistics() = {
+ val numBins = conf.histogramNumBins
+ val height = numElements.toDouble / numBins
+ val percentileArray = (0 to numBins).map(i => i * height).toArray
+
+ val binArray = new Array[HistogramBin](numBins)
+ var lowerIndex = percentileArray.head
+ var lowerBinValue = getRangeValue(0)
+ percentileArray.tail.zipWithIndex.foreach { case (upperIndex, binId) =>
+ // Integer index for upper and lower values in the bin.
+ val upperIndexPos = math.ceil(upperIndex).toInt - 1
+ val lowerIndexPos = math.ceil(lowerIndex).toInt - 1
+
+ val upperBinValue = getRangeValue(math.max(upperIndexPos, 0))
+ val ndv = math.max(upperIndexPos - lowerIndexPos, 1)
+ binArray(binId) = HistogramBin(lowerBinValue, upperBinValue, ndv)
+
+ lowerBinValue = upperBinValue
+ lowerIndex = upperIndex
+ }
+ Histogram(height, binArray)
+ }
+
+ // Utility method to compute histogram
+ private def getRangeValue(index: Int): Long = {
Review comment:
```
private def getRangeValue(index: Int): Long = {
assert(index >= 0, "index must be greater than and equal to 0")
if (step == 0) {
start + (numElements.toLong - index - 1) * step
} else {
start + index * step
}
}
```
?
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