[GitHub] [spark] viirya commented on a change in pull request #28764: [SPARK-21117][SQL] Built-in SQL Function Support - WIDTH_BUCKET

[GitBox <gi...@apache.org>]

viirya commented on a change in pull request #28764:
URL: https://github.com/apache/spark/pull/28764#discussion_r438451085



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala
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@@ -1325,3 +1325,94 @@ case class BRound(child: Expression, scale: Expression)
     with Serializable with ImplicitCastInputTypes {
   def this(child: Expression) = this(child, Literal(0))
 }
+
+object WidthBucket {
+
+  def computeBucketNumber(value: Double, min: Double, max: Double, numBucket: Long): jl.Long = {
+    // Checks error cases below:
+    //  - `numBucket` must be greater than zero and be less than Long.MaxValue
+    //  - `value`, `min`, and `max` cannot be NaN
+    //  - `min` bound cannot equal `max
+    //  - `min` and `max` must be finite
+    if (numBucket <= 0 || numBucket == Long.MaxValue || jl.Double.isNaN(value) || min == max ||
+        jl.Double.isNaN(min) || jl.Double.isInfinite(min) ||
+        jl.Double.isNaN(max) || jl.Double.isInfinite(max)) {
+      return null
+    }
+
+    val lower = Math.min(min, max)
+    val upper = Math.max(min, max)
+
+    if (min < max) {
+      if (value < lower) {
+        0L
+      } else if (value >= upper) {
+        numBucket + 1L
+      } else {
+        (numBucket.toDouble * (value - lower) / (upper - lower)).toLong + 1L
+      }
+    } else { // `min > max` case
+      if (value > upper) {
+        0L
+      } else if (value <= lower) {
+        numBucket + 1L
+      } else {
+        (numBucket.toDouble * (upper - value) / (upper - lower)).toLong + 1L
+      }
+    }
+  }
+}
+
+/**
+ * Returns the bucket number into which the value of this expression would fall
+ * after being evaluated.
+ *

Review comment:
       Should we also list the error cases in the expression description?




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