code: public static Pair<INDArray, INDArray> mergeLabels(@NonNull INDArray[][] labelsToMerge,
                      INDArray[][] labelMasksToMerge, int inOutIdx) {
          Pair<INDArray[], INDArray[]> p = selectColumnFromMDSData(labelsToMerge, labelMasksToMerge, inOutIdx);
          return mergeLabels(p.getFirst(), p.getSecond());
      }
docs: Extract out the specified column, and merge the specified label and label mask arrays
  (i.e., concatenate the examples)
  
  @param labelsToMerge     Features to merge. Will use featuresToMerge[all][inOutIdx]
  @param labelMasksToMerge Mask arrays to merge. May be null
  @return Merged features and mask. Mask may be null