Question

我有一个列表列表，需要将其与另一个列表列表合并。输入示例：答：[[1,2]，[3,4]，[5,6]，[7,8]] B：[[1,2]，[3,4]，[5,6]，[7,8]]

示例输出： [[1,2,1,2]，[1,2,3,4]，..，[7,8,5,6]，[7,8,7,8]]

2个列表列表，其中两个列表都包含4个列表，则会返回一个列表列表，大小为4 * 4 = 16

我已经尝试过递归地合并列表，但是我知道即使通过列表也行不通。

  mergeAll [[]] [[]] = [[]]
  mergeAll [[]] b = b
  mergeAll a [[]] = a
  mergeAll xs ys = mergeAll (merge xs ys) (drop 1 ys) 

  merge :: [[a]] -> [[a]] -> [[a]]
  merge [[]] [[]] = [[]]
  merge xs [[]] = xs
  merge [[]] ys = ys
  merge (x:xs) (y:ys)  = ((x++y):xs)

Answer 1

您可以使用列表理解：

[ xs ++ ys | xs <- listOfLists1, ys <- listOfLists2 ]

Answer 2

您可能会喜欢

Prelude> let doit = \as bs -> as >>= \a -> bs >>= \b -> pure (a ++ b)
Prelude> doit [[1,2],[3,4],[5,6],[7,8]] [[1,2],[3,4],[5,6],[7,8]]
[[1,2,1,2],[1,2,3,4],[1,2,5,6],[1,2,7,8],[3,4,1,2],[3,4,3,4],[3,4,5,6],[3,4,7,8],[5,6,1,2],[5,6,3,4],[5,6,5,6],[5,6,7,8],[7,8,1,2],[7,8,3,4],[7,8,5,6],[7,8,7,8]]

Answer 3

罗宾（Robin）在评论中说，您也可以这样做：

liftA2 (++)

我问自己a question，试图理解为什么这等同于：

[xs ++ ys | xs <- xss, ys <- yss]

如何将列表列表与列表列表结合起来

3 个答案: