Haskell：在元组列表中组合整数 [英] Haskell: Combine integers in a list of tuples

问题描述

我需要从这里得到：

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

到这里：

to here:

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

到目前为止，我有

So far I have

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

其中someFunc是我还需要弄清楚的一点并执行。我相信它应该利用foldr，map和/或intercalate来实现我的目标。任何想法？

where "someFunc" is the bit I still need to figure out and implement. I believe it should utilize foldr, map, and/or intercalate to accomplish my goal. Any ideas?

推荐答案

这应该是：

This should do:

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

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