code: public Frame trans() {
      int xrows = (int)_x.numRows();
      int xcols =      _x.numCols();
      Vec[] x_vecs = _x.vecs();
  
      // Currently cannot transpose factors due to domain mismatch
      for(int j = 0; j < xcols; j++) {
        if(x_vecs[j].isEnum())
          throw H2O.unimpl();
      }
  
      Vec[] output = new Vec[xrows];
      String[] names = new String[xrows];
      for(int i = 0; i < xrows; i++) {
        output[i] = Vec.makeSeq(xcols);
        names[i] = "C" + String.valueOf(i+1);
      }
  
      for(int i = 0; i < xrows; i++) {
        for(int j = 0; j < xcols; j++) {
          double d = x_vecs[j].at(i);
          output[i].set(j, d);
        }
      }
      return new Frame(names, output);
    }
docs: Transpose