def clean_list(l):
    """
    Clean the list with delete negative values to not display them

    :param l: list to browse
    :return: modified list
    """
    for j in range(0, len(l)):
        for i in range(0, len(l[0])):
            if l[j][i] == -0.5 or l[j][i] == -1:
                l[j][i] = None
    return l