是否可以简化以下Linq表达式? [英] Is it possible to simplify the following Linq expression?

问题描述

我必须维护一个代码，以比较两个集合的项目

I have to maintain a code that makes a comparison between the items of two collections

list1.Where(item1 => list2.Any(item2 => Cond1(item1,item2)) &&
    !list2.Any(item2 => Cond2(item1,item2)) 
)

我试图简化所有这些迭代，我想知道上面的代码是否等同于下面的代码

I was trying to simplify all those iterations and I wondered whether the above code is equivalent to the following

list1.Where(item1 => list2.Any(item2 => Cond1(item1,item2) && !Cond2(item1,item2)))

这似乎更易于管理，所以我尝试了一些测试用例，初步结果还可以.您是否认为总体上是正确的，还是可以发现需要第一个较长的代码(与第二个较短的代码不同)的情况?

That seems more manageable, so I tried with some test cases and the initial results were ok. Do you think that it is true in general or can you spot a situation where the first, longer code is needed (=different from the second, shorter one)?

评论中的一些有趣注释.

Some interesting notes from the comments.

1. 当且仅当Cond1确定list2的唯一键条件时，上述内容才是等效的，但是在通常情况下，这是不正确的.
2. 反转两个Any语句的顺序似乎更有效，因为

1. the above seems to be equivalent if and only if Cond1 determines a unique key condition for list2, but of course this is not true in the general case.
2. inverting the order of the two Any statement appears to be more efficient as pointed out by Knoop.

关于第2点，请考虑使用更现实的业务代码

Regarding point 2, please consider that a more realistic business code would be

list1.Where(item1 => list2.Any(item2 => Cond1(item1,item2)) &&
    !list2.Any(item2 => Cond1(item1,item2) && Cond2(item1,item2)) 
)

因为这里描述的典型业务问题是比较两个集合并寻找缺失，匹配和不同的记录，而后者(不同但不是缺失的记录)就是问题中报告的内容

because the typical business problem described here is comparing 2 collections and looking for missing, matching and different records, the latter (different - but not missing - records) being what is reported in the question

推荐答案

这里描述的典型业务问题是比较两个集合，并寻找缺失，匹配和不同的记录，后者(不同但不是缺失的记录)是问题中所报告的内容

the typical business problem described here is comparing 2 collections and looking for missing, matching and different records, the latter (different - but not missing - records) being what is reported in the question

如果您既想要功能又高效的解决方案，则可以使用Enumerable.Aggregate LINQ扩展方法，如类似的 answer中所建议，在第一个集合list1上包裹在外部Where中.

If you want both a functional and an efficient solution you can use the Enumerable.Aggregate LINQ extension method, as suggested in a similar answer, wrapped inside the external Where over the first collection list1.

(bool allVerified, bool anyVerified) = 
    list2.Aggregate( 
        ValueTuple.Create(true, false), 
        (tuple, item) => ValueTuple.Create(
            tuple.Item1 && !(Cond1(item1,item) && Cond2(item1,item)), 
            tuple.Item2 || Cond1(item1, item)) );
return allVerified && anyVerified;

完整摘要小提琴在这里.

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