copy small part of mat to another

I can't figure how to copy a part of mat to another mat. ( or to itself) I want for example to copy (or to keep) only the first row of srcMat. I am using : for ( int x = 0; x < height; x++ ) { for ( int y = 0; y < width; y++ ) { destMat = scrMat.at(0,y); // or destMat.at(x,y) = scrMat.at(0,y); } } I am not sure about using: srcMat.copyTo( destMat( Rect( y, 0, srcMat.cols, srcMat.rows ) ) );