Question

是否有标准函数来列举一个F#序列, 其功能如 Python s enumberate () ?

这很容易从零开始写作:

let enumerate (sq : seq< T>) = seq {
    let rec loop (e : IEnumerator< T>) index = seq {
        if e.MoveNext() then 
            yield (index, e.Current)
            yield! loop e (index+1) 
    }

    use enum = sq.GetEnumerator()
    yield! loop enum 0
    }

但我不想重塑轮子

PS:还有,我试过

let seasons = ["Spring"; "Summer"; "Fall"; "Winter"]
for x in Seq.zip [0..100000] seasons do
    printfn "%A" x

但此 [0. 10000] 部分看起来很丑陋。

Answer 1

我想你可能想要 Seq.mapi 或 Seq.iteri 。

http://msdn.microsoft.com/en-us/library/ee3404331.aspx" rel=“noreferrer'>http://msdn.microsoft.com/en-us/library/ee340431.aspx

http://msdn.microsoft.com/en-us/library/ee370541" rel="noreferrer">http://msdn.microsoft.com/en-us/library/ee370541

Answer 2

这就是你想要的:

module Seq =
    let inline enumerate source = Seq.mapi (fun i x -> i,x) source

> ["a"; "b"] |> Seq.enumerate;;
val it : seq<int * string> = seq [(0, "a"); (1, "b")]

或热nspicy与FSharpx:

let enumerate source = Seq.mapi (curry id) source

实际上,在FSharpx中,它已经作为 Seq.index 提供。

友情链接