public int[] currentScratchColumns() {
      TreeSet<Integer> treeSet = new TreeSet<>();
      for (Integer col : usedOutputColumns) {
        treeSet.add(initialOutputCol + col);
      }
      return ArrayUtils.toPrimitive(treeSet.toArray(new Integer[0]));
    }
Context class for vectorization execution.
Main role is to map column names to column indices and serves as a
factory class for building vectorized expressions out of descriptors.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java