OCaml:过滤映射并将值放入列表中 [英] OCaml : filter map and put the values into a list

问题描述

我可以通过以下方式过滤我的地图关键:

I can filter my map by key :

module PairKeys =
struct
  type t = string * string
  let compare (x0,y0) (x1,y1) =
    match String.compare x0 x1 with
    | 0 -> String.compare y0 y1
    | c -> c
end

module StringMap = Map.Make(PairKeys);;
....

let put_key_values_into_a_list (key_searched : string) = 
    StringMap.filter (fun key -> key = key_searched)
(* should return a list of the values in the filtered map *)

在那之后，我想将这些值放入一个列表中.我怎样才能在 OCaml 中做到这一点?

After that, I want to put the values into a list. How can I do this in OCaml?

Map.Make 文档:http://caml.inria.fr/pub/docs/manual-ocaml/libref/Map.Make.html

Map.Make documentation : http://caml.inria.fr/pub/docs/manual-ocaml/libref/Map.Make.html

谢谢

推荐答案

您可以使用 bindings 来检索映射的键/值对，然后进一步处理它们以提取值.例如:

You can use bindings to retrieve the key/value pairs of a map and then further process them to extract the values. For example:

let put_key_values_into_a_list key_searched map =
    MyMap.filter (fun key _ -> key = key_searched) map
    |> MyMap.bindings |> List.split |> snd

我们使用 List.split 将一对列表转换为一对列表(一个包含键，一个包含值)，然后 snd 提取列表值.

We use List.split to convert a list of pairs into a pair of lists (one containing the keys, one the values) and then snd to extract the list of values.

还要注意 filter 接受一个带有两个参数的函数(这里忽略第二个参数).

Note also that filter takes a function with two arguments (the second of which gets ignored here).

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