def split_curves(curves, param):
    """Split curves into lists sorted by the given parameter

    Parameters
    ----------
    curves : array_like of Curve
        all curves
    param : str
        key of parameter to sort after

    Returns
    -------
    split_curves : list of list of Curve
    """
    out = {}
    for curve in curves:
        val = curve.params[param]
        if val not in out.keys():
            out.update({val: [curve]})
        else:
            out[val].append(curve)
    return list(out.values())