C#ToDictionary Lambda选择索引和元素?

问题描述

我有一个像string strn = "abcdefghjiklmnopqrstuvwxyz"这样的字符串，并且想要一个像这样的字典:

I have a string like string strn = "abcdefghjiklmnopqrstuvwxyz" and want a dictionary like:

Dictionary<char,int>(){
    {'a',0},
    {'b',1},
    {'c',2},
    ...
}

我一直在尝试

strn.ToDictionary((x,i) => x,(x,i)=>i);

...但是我一直在遇到关于委托不接受两个参数和未指定参数等的各种错误.

...but I've been getting all sorts of errors about the delegate not taking two arguments, and unspecified arguments, and the like.

我做错了什么?

与答案相比，我更希望有提示，因此我对下一次需要做的事情有心理上的了解，但是根据Stackoverflow的性质，答案也很好.

I would prefer hints over the answer so I have a mental trace of what I need to do for next time, but as per the nature of Stackoverflow, an answer is fine as well.

推荐答案

首先使用.Select运算符:

strn
    .Select((x, i) => new { Item = x, Index = i })
    .ToDictionary(x => x.Item, x => x.Index);

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