[GitHub] [spark] beliefer commented on a diff in pull request #38874: [SPARK-41235][SQL][PYTHON]High-order function: array_compact implementation

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

beliefer commented on code in PR #38874:
URL: https://github.com/apache/spark/pull/38874#discussion_r1043982018


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala:
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@@ -4600,3 +4600,57 @@ case class ArrayExcept(left: Expression, right: Expression) extends ArrayBinaryL
   override protected def withNewChildrenInternal(
     newLeft: Expression, newRight: Expression): ArrayExcept = copy(left = newLeft, right = newRight)
 }
+
+@ExpressionDescription(
+  usage = "_FUNC_(array) - Removes null values from the array.",
+  examples = """
+    Examples:
+      > SELECT _FUNC_(array(1, 2, 3, null));
+       [1,2,3]
+  """,
+  group = "array_funcs",
+  since = "3.4.0")
+case class ArrayCompact(child: Expression)
+  extends UnaryExpression with ExpectsInputTypes with NullIntolerant {
+  override def inputTypes: Seq[AbstractDataType] = Seq(ArrayType)
+  override def dataType: DataType = child.dataType
+
+  @transient private lazy val elementType: DataType = dataType.asInstanceOf[ArrayType].elementType
+
+  override def nullSafeEval(array: Any): Any = {
+    val newArray = new Array[Any](array.asInstanceOf[ArrayData].numElements())
+    var pos = 0
+    var hasNull = false
+    array.asInstanceOf[ArrayData].foreach(elementType, (index, v) =>
+      // add elements only if the source has null
+      if (v != null && hasNull) {
+        newArray(pos) = v
+        pos += 1
+      } else if (v == null && !hasNull) {
+        hasNull = true
+        // source has null elements, so copy the elements to newArray
+        for(i <- 0 until index) {
+          newArray(pos) = array.asInstanceOf[ArrayData].get(i, elementType)
+          pos += 1
+        }
+      }
+    )
+    if (hasNull) {
+      new GenericArrayData(newArray.slice(0, pos))
+    } else {
+      array
+    }
+  }
+  override def prettyName: String = "array_compact"
+
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
+
+    nullSafeCodeGen(ctx, ev, array => {
+      val expr = ctx.addReferenceObj("arrayCompactExpr", this)
+      s"${ev.value} = (ArrayData)$expr.nullSafeEval($array);"

Review Comment:
   This implementation has some hackers. Please see the discussion https://github.com/apache/spark/pull/38865#discussion_r1043977011



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