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