Question

我正在尝试学习Haskell，但我无法找到解决以下问题的方法。

考虑以下类型为ourFunction :: [[String]] -> [[String]]的函数当两个伴随字符串相同时，它们应更改为'x'。示例：

ourFunction[["a","b","c","d"],[["e","f","a","d"]

a b c d
e f a d

它应该返回[["a","b","c","x"],[["e","f","a","x"]。

我要求它理解列表索引并更改函数列表中的值。

Answer 1

假设

中的列表相同

import Data.List

test = replaceWithxForEqualIndexes [["a","b","c","d"],["e","f","a","d"]]
--Here is the magic, transpose so you get same indexes in the same list,
--then check for equality and replace if equals, then transpose back
replaceWithxForEqualIndexes x = transpose $ map ifSameChangeToX $ transpose x

ifSameChangeToX x = ifSameChangeTo x "x"

ifSameChangeTo :: (Eq a) => [a] -> a -> [a]
ifSameChangeTo x rep
    | allTheSame x = take (length x) (repeat rep)
    | otherwise = x

allTheSame :: (Eq a) => [a] -> Bool
allTheSame xs = and $ map (== head xs) (tail xs)

Answer 2

import Data.List

ourFunction :: [[String]] -> [[String]]
ourFunction input = [fst result, snd result]
  where result = unzip $ zipWith (\x y -> if x == y then ("x", "x") else (x, y)) (head input) (last input)

函数在Haskell中使用双列表

2 个答案: