C# LINQ、Where() 与 FindAll()
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LINQ, Where() vs FindAll()
提问by Grant
Can someone explain how the LINQ functions Where(..) and FindAll(..) differ? They both seem to do the same thing...
有人能解释一下 LINQ 函数 Where(..) 和 FindAll(..) 的区别吗？他们似乎都在做同样的事情......
采纳答案by Adam Robinson
FindAll()is a function on the List<T>type, it's not a LINQ extension method like Where. The LINQ extension methods work on any type that implements IEnumerable, whereas FindAllcan only be used on List<T>instances (or instances of classes that inherit from it, of course).
FindAll()是List<T>类型上的函数，它不是像Where. LINQ 扩展方法适用于实现 的任何类型IEnumerable，而FindAll只能用于List<T>实例（或从它继承的类的实例，当然）。
Additionally, they differ in actual purpose. Wherereturns an instance of IEnumerablethat is executed on-demand when the object is enumerated. FindAllreturns a new List<T>that contains the requested elements. FindAllis more like calling Where(...).ToList()on an instance of IEnumerable.
此外，它们在实际用途上有所不同。Where返回一个IEnumerable在枚举对象时按需执行的实例。FindAll返回一个List<T>包含请求元素的新元素。FindAll更像是调用Where(...).ToList()上的一个实例IEnumerable。
回答by WayneC
If I recall correctly, the main difference (besides what they're implemented on: IEnumerable<T>vs. List<T>) is that Whereimplements deferred execution, where it doesn't actually do the lookup until you need it -- using it in a foreach loop for example. FindAllis an immediate execution method.
如果我没记错的话，主要区别（除了它们在：IEnumerable<T>vs.上实现的内容之外List<T>）是Where实现延迟执行，在您需要之前它实际上不会进行查找 - 例如在 foreach 循环中使用它。 FindAll是一种立即执行的方法。
回答by cfern
The biggest difference to me is that .FindAll is also available in .Net 2.0. I don't always have the luxury to program in .Net 3.5, so I try to remember the 'native' methods of the .Net generic collections.
对我来说最大的不同是 .FindAll 也可以在 .Net 2.0 中使用。我并不总是有幸在 .Net 3.5 中编程，所以我尝试记住 .Net 泛型集合的“本机”方法。
It happened several times that I implemented an already available List method myself because I couldn't LINQ it.
有几次我自己实现了一个已经可用的 List 方法，因为我不能 LINQ 它。
What I find handy in this case is that, using VS2008, I canuse type inference and the lambda syntax. These are compiler features, not framework features. This means I can write this and still remain within .Net 2.0:
在这种情况下，我觉得很方便的是，使用 VS2008，我可以使用类型推断和 lambda 语法。这些是编译器特性，而不是框架特性。这意味着我可以写这个并且仍然保留在 .Net 2.0 中：
var myOddNums = myNums.FindAll(n => n%2==1);
But if you do have LINQ available, keeping the difference between deferred execution and immediate execution is important.
但是，如果您确实有可用的 LINQ，那么保留延迟执行和立即执行之间的区别很重要。
回答by digiben
I did some tests on a list of 80K objects and found that Find()can be up to 1000% faster than using a Wherewith FirstOrDefault(). I didn't know that until testing a timer before and after each call. Sometimes it was the same time, other times it was faster.
我对一个包含 80K 个对象的列表进行了一些测试，发现它Find()比使用Wherewith快 1000% FirstOrDefault()。直到在每次通话之前和之后测试计时器之前，我都不知道这一点。有时是相同的时间，有时会更快。
