按F#中的元组分组 [英] Group by with tuples in F#

问题描述

假设我有一个这样的tupples列表:

Suppose I have a list of tupples like these :

[("A",12); ("A",10); ("B",1);  ("C",2); ("C",1)]

我想做某种groupby我该如何处理?

And I would like to do some kind of groupby how do I handle that?

在伪代码SQL中，它看起来应该像这样:

In pseudocode-SQL it should look something like this :

SELECT fst(tpl), sum(lst(tpl)) FROM [TupplesInList] GROUP BY fst(tpl)

屈服

 [("A",22); ("B",1); ("C",3)]

如果键存在，我可以制作一个Dictionary并添加整数，但是我很难相信这将是像F#这样具有表现力的语言的最佳解决方案.

I could make a Dictionary and add the ints if the key exist, but I can hardly believe that would be the best solution in a language as expressive as F#.

推荐答案

一种解决方案:

let tuples = [("A",12); ("A",10); ("B",1);  ("C",2); ("C",1)]
tuples 
|> Seq.groupBy fst 
|> Seq.map (fun (key, values) -> (key, values |> Seq.sumBy snd))

...或不使用管道:

...or without piping:

let tuples = [("A",12); ("A",10); ("B",1);  ("C",2); ("C",1)]
Seq.map (fun (key, group) -> key, Seq.sumBy snd group)
        (Seq.groupBy fst tuples)

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