我可以在LINQ中增加计数变量吗?

问题描述

我想做这样的事情:

from a in stuff
let counter = 0
select new { count = counter++, a.Name };

但是我收到一个错误消息，告诉我计数器是只读的.有没有一种方法可以执行类似的操作，而无需在查询外部声明变量?

But I get a error telling me that counter is read only. Is there a way to do something similar to this, without declaring a variable outside of the query?

基本上，我只想在 LINQPad 中显示一个计数/索引列(太棒了，顺便说一句) ，这意味着我无法提前声明计数器.

Basically, I just want to show a count/index column in LINQPad (which is awesome, BTW), which means I can't declare counter ahead of time.

推荐答案

不是使用副作用，而是使用Select的重载，该重载需要一个索引:

Rather than using side-effects, use the overload of Select which takes an index:

stuff.Select((value, index) => new { index, value.Name });

您可以使用副作用来做到这一点，但不能以您尝试的方式来做到:

You could do it using side-effects, but not in the way you tried:

int counter = 0;
var query = from a in stuff
            select new { count = counter++, a.Name };

尽管如此，我还是强烈建议.

I would strongly advise against this though.

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