旋轉或壓縮序列 <seq<'a> &gt;在F＃中

Question

假設我有一個序列序列，例如

{1, 2, 3}, {1, 2, 3}, {1, 2, 3}

樞轉或壓縮此序列的最佳方法是什么，所以我有了

{1, 1, 1}, {2, 2, 2}, {3, 3, 3}

是否有一種可理解的方式來實現，而無需借助對基礎IEnumerator<_>類型的操縱？

為了澄清起見，這些是seq<seq<int>>對象。 每個序列（內部和外部）都可以具有任意數量的項目。

Answer 1

如果您要使用語義上為Seq的解決方案，則必須一直保持懶惰。

let zip seq = seq
            |> Seq.collect(fun s -> s |> Seq.mapi(fun i e -> (i, e))) //wrap with index
            |> Seq.groupBy(fst) //group by index
            |> Seq.map(fun (i, s) -> s |> Seq.map snd) //unwrap

測試：

let seq =  Enumerable.Repeat((seq [1; 2; 3]), 3) //don't want to while(true) yield. bleh.
printfn "%A" (zip seq)

輸出：

seq [seq [1; 1; 1]; seq [2; 2; 2]; seq [3; 3; 3]]

Answer 2

這似乎很不雅致，但它得到了正確的答案：

(seq [(1, 2, 3); (1, 2, 3); (1, 2, 3);]) 
|> Seq.fold (fun (sa,sb,sc) (a,b,c) ->a::sa,b::sb,c::sc) ([],[],[]) 
|> fun (a,b,c) -> a::b::c::[]

Answer 3

它看起來像矩陣轉置。

let data =
    seq [
        seq [1; 2; 3]
        seq [1; 2; 3]
        seq [1; 2; 3]
    ]

let rec transpose = function
    | (_::_)::_ as M -> List.map List.head M :: transpose (List.map List.tail M)
    | _ -> []

// I don't claim it is very elegant, but no doubt it is readable
let result =
    data
    |> List.ofSeq
    |> List.map List.ofSeq
    |> transpose
    |> Seq.ofList
    |> Seq.map Seq.ofList

另外，您可以對seq采用相同的方法，這要歸功於優雅的Active模式的答案 ：

let (|SeqEmpty|SeqCons|) (xs: 'a seq) =
  if Seq.isEmpty xs then SeqEmpty
  else SeqCons(Seq.head xs, Seq.skip 1 xs)

let rec transposeSeq = function
    | SeqCons(SeqCons(_,_),_) as M ->
        Seq.append
            (Seq.singleton (Seq.map Seq.head M))
            (transposeSeq (Seq.map (Seq.skip 1) M))
    | _ -> Seq.empty

let resultSeq = data |> transposeSeq

另請參閱此答案以獲取技術細節和兩個參考： PowerPack的Microsoft.FSharp.Math.Matrix和涉及可變數據的另一種方法。

Answer 4

這和@Asti的答案是一樣的，只是清理了一下：

[[1;2;3]; [1;2;3]; [1;2;3]] 
    |> Seq.collect Seq.indexed 
    |> Seq.groupBy fst 
    |> Seq.map (snd >> Seq.map snd);;