code: public SparseDoubleVector getRowVector(int row) {
          SparseDoubleVector v = rowToColumns.get(row);
          return (v != null)
              ? Vectors.subview(v, 0, cols)
              : Vectors.subview(emptyVector, 0, cols);
      }
docs: Returns a {@link DoubleVector} of the contents of the row.  The length of
  the returned row vector reflects the size of matrix at the time of the
  call, which may be different from earlier calls to {@link #columns()}.
  
  @param row {@inheritDoc}
  @return {@inheritDoc}