f# - 在 F# 中寻找 Haskell `group` 替代方案

Question

Haskell group 描述如下:http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v:group

示例:

group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"]

有简单的 F# 方法吗？

我可以实现类似的东西

let rec sameCounter (data : list<float>) el same (ss : list<float * int>) = 
    if data.Length > (el + 1) then
        if data.[el] = data.[el + 1] then
                              sameCounter data (el + 1) <| same + 1  <| ss
        else if same > 0 then sameCounter data (el + 1) <| 0         <| (data.[el], same) :: ss
             else             sameCounter data (el + 1) <| 0         <| ss
    else ss
let group d = sameCounter d 0 0 []

但我认为这有点难看，有更好的变体吗？

Answer 1

这是我想出来的，我认为是合理的:

let groupConsecutive sq =
    (Array.ofSeq sq, [])
    ||> Array.foldBack (fun x -> function
        | [] -> [[x]]
        | xs :: xss ->
            if x = List.head xs then
                (x :: xs) :: xss
            else [x] :: xs :: xss)
// val groupConsecutive : s:seq<'a> -> 'a list list when 'a : equality

groupConsecutive "Mississippi"
// val it : char list list = [['M']; ['i']; ['s'; 's']; ['i']; ['s'; 's']; ['i']; ['p'; 'p']; ['i']]

如果您还希望能够获取和返回无限序列，则需要手动使用GetEnumerator，这会变得更加难看。