Haskell：组合元组列表中的整数

Question

我需要从这里出发：

[(2,"a"), (1,"a"), (1,"b"), (1,"c"), (2,"dd")]

到这里：

[([1, 2], "a"), ([1], "b"), ([1], "c"), ([2], "dd")]

到目前为止我有

combineInts listTuple = someFunc (map (\(num, str) -> ([num], str)) listTuple)

其中 "someFunc" 是我仍然需要弄清楚并实施的部分。我相信它应该利用 foldr、map、and/or intercalate 来实现我的目标。有什么想法吗？

Answer 1

如果您先订购列表，则可以使用 groupBy 执行此操作：

import Data.List (groupBy)
import Data.Ord (comparing)
import Data.Function (on)

map (\l@((_,c):_) -> (map fst l, c))  $ groupBy (on (==) snd) $ sortBy (comparing snd) inputList

Answer 2

应该这样做：

import Data.Function (on)
import Data.List (groupBy, sort, sortBy)

out = map f . groupBy ((==) `on` snd) . sortBy (compare `on` snd) $ input
  where input = [(2,"a"),(1,"a"),(1,"b"),(1,"c"),(2,"dd")]
        f xs@(x:_) = (sort $ map fst xs, snd x)

main = print out

Haskell：组合元组列表中的整数

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