float similarity( Row r )
    {
        float sim = 0.0f;
        float fullSim = 1.0f/cells.size();
        for ( int i=0;i<cells.size();i++ )
        {
            FragList fl1 = cells.get(i);
            FragList fl2 = r.cells.get(i);
            if ( fl1.merged&&fl2.merged )
                sim += fullSim;
            else if ( fl1.equals(fl2) )
                sim += fullSim;
            else
                sim += fl1.similarity(fl2)/cells.size();
        }
        return sim;
    }