将选项类型列表缩减为仅非元素的最佳方式？ [英] Best way to condense a list of option type down to only elements that are not none?

问题描述

我出乎意料地从一个选项列表中删除了一个列表，这个列表只包含了一些元素。

我的初始尝试是：

  let ga = List.filter（fun xx  - > 
 match xx with 
 | Some（g） - > true 
 | None  - > false）gao 
  

但是，当然，这个结果类型仍然是一个选项列表。我不知道如何使用List.map来压缩这个，因为你必须处理匹配语句中的所有情况。丑陋的：

  let rec gOptRemove gdec gacc = 
匹配gdec和
 | head :: tail  - > 
与
 |匹配头部一些（a） - > gOptRemove tail（a :: gacc）
 |无 - > gOptRemove tail gacc 
 | []  - > gacc 
  

我宁愿找到一个非递归解决方案或找出标准方法是什么

解决方案

简单地

  List.choose id 
  

如

 > [有些4;没有;一些2;无] |> List.choose id ;; 
 val it：int list = [4; 2] 
  

List.choose

id

I'm unexpectedly having a bit of trouble with going from a list of 'a option down to a list containing only the elements that are Some.

My initial attempt was:

    let ga = List.filter (fun xx ->
        match xx with
        | Some(g) -> true
        | None -> false) gao 

But of course, this result type is still 'a option list. I don't know how to use List.map to condense this, because you have to handle all cases in a match statement. I have an ugly solution, but I'm wondering if there is something better.

Ugly:

    let rec gOptRemove gdec gacc = 
        match gdec with 
        | head :: tail -> 
            match head with 
            | Some(a) -> gOptRemove tail (a :: gacc)
            | None -> gOptRemove tail gacc
        | [] -> gacc

I would prefer to find a non-recursive solution or find out what the standard way is for this kind of thing.

解决方案

Simply

List.choose id

as in

> [Some 4; None; Some 2; None] |> List.choose id;;
val it : int list = [4; 2]

List.choose

id

这篇关于将选项类型列表缩减为仅非元素的最佳方式？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！