@SuppressWarnings("unchecked")
  protected static Operator<? extends OperatorDesc> getParent(Stack<Node> stack) {
    return (Operator<? extends OperatorDesc>)Utils.getNthAncestor(stack, 1);
  }
Returns the parent operator in the walk path to the current operator.

@param stack The stack encoding the path.

@return Operator The parent operator in the current path.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/physical/BucketingSortingOpProcFactory.java