def _separate_ghosts_from_histogram(H_in):
    """
    Create two disjunct dictionaries from H_in, one (H) containing the real
    species histograms, another (Hx) containing the X particle histograms.
    """
    H = {}
    Hx = {}
    for key in H_in:
        if (key == 'radii'):
            H[key] = H_in[key].copy()
            Hx[key] = H_in[key].copy()
            continue
        if ('X' in key):
            Hx[key] = H_in[key].copy()
        else:
            H[key] = H_in[key].copy()
    return (H, Hx)