Github user ueshin commented on a diff in the pull request:

    https://github.com/apache/spark/pull/21208#discussion_r186007739
  
    --- Diff: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
 ---
    @@ -1229,3 +1229,140 @@ case class Flatten(child: Expression) extends 
UnaryExpression {
     
       override def prettyName: String = "flatten"
     }
    +
    +/**
    + * Returns the array containing the given input value (left) count (right) 
times.
    + */
    +@ExpressionDescription(
    +  usage = "_FUNC_(element, count) - Returns the array containing element 
count times.",
    +  examples = """
    +    Examples:
    +      > SELECT _FUNC_('123', 2);
    +       ['123', '123']
    +  """)
    +case class ArrayRepeat(left: Expression, right: Expression)
    +  extends BinaryExpression with ExpectsInputTypes {
    +
    +  override def dataType: ArrayType = ArrayType(left.dataType, 
left.nullable)
    +
    +  override def inputTypes: Seq[AbstractDataType] = Seq(AnyDataType, 
IntegerType)
    +
    +  override def nullable: Boolean = right.nullable
    +
    +  override def eval(input: InternalRow): Any = {
    +    val count = right.eval(input)
    +    if (count == null) {
    +      null
    +    } else {
    +      new 
GenericArrayData(List.fill(count.asInstanceOf[Int])(left.eval(input)))
    --- End diff --
    
    We should evaluate `left.eval(input)` before `List.fill()()` because 
`List.fill()()` evaluates the second argument every time.
    
    Btw, `Array.fill()()` instead of `List.fill()()`?


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