'drop_idx is only available if sparse=False
drop_idx is supposed to index into uni'

def dummy(self, drop_idx=None, sparse=False, dtype=int):

    uni = self.uni
    if (drop_idx is not None):
        idx = lrange(len(uni))
        del idx[drop_idx]
        uni = uni[idx]
    group = self.group
    if (not sparse):
        return (group[:, None] == uni[None, :]).astype(dtype)
    else:
        return dummy_sparse(self.group_int)
