列表/序列中的F＃词典生成器

Question

Is there a constructor for Dictionary in F# (that takes a Seq/List as input, and output a Dictionary)? I have written the following code that does what I want, but I am just curious maybe it is already implemented (and so I don't need to implement it myself)

let DictionaryBuilder (keyFunc:'a->'b) (valueFunc:'a->'c) aList =
    let dict = new Dictionary<'b,'c>()
    aList 
    |> Seq.iter (fun a -> dict.Add(keyFunc a, valueFunc a ))
    dict    // return

I know that in C#, you can use .ToDictionary (using System.Linq)

// using System.Collections.Generic;
// using System.Linq;
List<string> example = new List<string> {"a","b","c"};
Dictionary<string,string> output = example.ToDictionary(x => x+"Key", x => x+"Value");
// Output: {"aKey": "aValue", "bKey": "bValue", "cKey": "cValue"}

Thank you very much.

Answer 1

The signature of the dict function it's as follows:

dict : seq<'Key * 'Value> -> IDictionary<'Key,'Value> 

So it takes a key value sequence as input. The key here would be to give it a key value sequence. In your case, you could use map instead of iter. The lines of code will be similar but it's a more functional way.

aList 
|> Seq.map (fun a -> keyFunc a, valueFunc a )
|> dict

Edit

As TheQuickBrownFox have noted in the comments, the dict function produces a read-only dictionary.

Answer 2

I would recommend that you just use LINQ:

open System.Linq
[1; 2; 3].ToDictionary(id, (*) 2)

Either use it directly or use it in your helper function if you'd rather use a function than an extension method.

module Seq =
    open System.Linq
    let toDictionary (f:'s -> 'k) (g:'s -> 'v) (xs:_ seq) = xs.ToDictionary(f, g)