[GitHub] [spark] viirya commented on a change in pull request #24073: [SPARK-27134][SQL] array_distinct function does not work correctly with columns containing array of array

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viirya commented on a change in pull request #24073: [SPARK-27134][SQL] array_distinct function does not work correctly with columns containing array of array
URL: https://github.com/apache/spark/pull/24073#discussion_r265064221
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
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 @@ -3112,29 +3112,30 @@ case class ArrayDistinct(child: Expression)
     (data: Array[AnyRef]) => new GenericArrayData(data.distinct.asInstanceOf[Array[Any]])
   } else {
     (data: Array[AnyRef]) => {
-      var foundNullElement = false
-      var pos = 0
+      val arrayBuffer = new scala.collection.mutable.ArrayBuffer[Any]
+      var alreadyStoredNull = false
+      var found = false
       for (i <- 0 until data.length) {
-        if (data(i) == null) {
-          if (!foundNullElement) {
-            foundNullElement = true
-            pos = pos + 1
+        if (data(i) != null) {
+          found = false
+          var j = 0;
+          while (!found && j < arrayBuffer.size) {
+            val va = arrayBuffer(j)
+            found = (va != null) && ordering.equiv(va, data(i))
+            j += 1
           }
-        } else {
-          var j = 0
-          var done = false
-          while (j <= i && !done) {
-            if (data(j) != null && ordering.equiv(data(j), data(i))) {
-              done = true
-            }
-            j = j + 1
+          if (!found) {
+            arrayBuffer += data(i)
           }
-          if (i == j - 1) {
-            pos = pos + 1
+        } else {
+          // De-duplicate the null values.
+          if (!alreadyStoredNull) {
+            arrayBuffer += data(i)
+            alreadyStoredNull = true
           }
         }
       }
-      new GenericArrayData(data.slice(0, pos))
 
 Review comment:
   Looks like original implementation assumes the duplicate items are placed at the end of `data`? I think it not only affects array of array, but also other element type like `BinaryType`.

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