code: public static Frame transpose(Frame src, Frame tgt){
      if(src.numRows() != tgt.numCols() || src.numCols() != tgt.numRows())
        throw new IllegalArgumentException("dimension do not match!");
      for(Vec v:src.vecs()) {
        if (v.isCategorical())
          throw new IllegalArgumentException("transpose can only be applied to all-numeric frames (representing a matrix)");
        if(v.length() > 1000000)
          throw new IllegalArgumentException("too many rows, transpose only works for frames with < 1M rows.");
      }
      new TransposeTsk(tgt).doAll(src);
      return tgt;
    }
docs: Transpose the Frame as if it was a matrix (rows <-> columns).
  Must be all numeric, will fail if there are too many rows ( >= ~.5M).
  
  Result is made to be compatible (i.e. the same vector group and chunking) with the target frame.
  
  @param src
  @return