def events_to_map(shifts):
    """
    Convert a list of shifts to a map of shifts
    """
    shift_map = {}
    for shift in shifts:
        start_date = shift['start_dt']
        if start_date in shift_map:
            shift_map[start_date].append(shift)
        else:
            shift_map[start_date] = [shift]
    return shift_map