笛卡尔在Erlang中的列表列表的产品

Question

我有一个列表列表(在erlang中,字符串是列表),如下所示:

[ "ABC", "DEF"]

我希望在函数返回的列表中获得以下组合:

["ad","ae","af","bd","be","bf","cd","ce","cf"]

是否可以使用列表理解？我事先不知道列表的维度

Answer 1

如果您不知道输入的维度,那么您需要使用递归,因为@legoscia说:

cartesian([H])   -> [[A] || A <- H];
cartesian([H|T]) -> [[A|B] || A <- H, B <- cartesian(T)].

1-dim输入"abc"变为["a","b","c"],其他一切都是递归.

> cartesian:cartesian(["abc", "def", "ghi"]).
 ["adg","adh","adi","aeg","aeh","aei","afg","afh","afi",
 "bdg","bdh","bdi","beg","beh","bei","bfg","bfh","bfi","cdg",
 "cdh","cdi","ceg","ceh","cei","cfg","cfh","cfi"]

编辑:或者更简单,但是:让0-dim参数返回包含空集的集合.我认为这也是数学家所做的.

cartesian([H|T]) -> [[A|B] || A <- H, B <- cartesian(T)];
cartesian([]) -> [[]].