def strip_id_from_matrix(mat):
    """
    Remove the ID (1st row element) form a matrix

    :param mat: a 2D list

    :rtype: a 2D list with the 1st row elelemnt (ID) removed
    """
    new_mat = []
    for i in range(0, len(mat)):
        new_mat.append(mat[i][1:])
    return new_mat