二显著差异：

• 查找是不可改变的。耶:)（至少，我认为具体的查找类是不可变的，而 ILookup 接口没有提供任何变异的成员，有可以的是其他可变实现的，当然。）


• 当你查找一个关键这是不是在查找present，你会得到一个空的顺序背，而不是 KeyNotFoundException 。 （因此没有 TryGetValue ，AFAICR。）

• Lookup is immutable. Yay :) (At least, I believe the concrete Lookup class is immutable, and the ILookup interface doesn't provide any mutating members. There could be other mutable implementations, of course.)
• When you lookup a key which isn't present in a lookup, you get an empty sequence back instead of a KeyNotFoundException. (Hence there's no TryGetValue, AFAICR.)

他们可能是在效率等同 - 查找可能使用词典＆LT; TKEY的，GroupingImplementation＆LT; TValue＆GT;＆GT; 的场景，例如落后。根据您的要求二者之间做出选择。我个人而言，查找通常是一个比一个更适合词典＆LT; TKEY的，列表与LT; TValue＆GT;＆GT; ，主要是由于上面的第一个两分。

They're likely to be equivalent in efficiency - the lookup may well use a Dictionary<TKey, GroupingImplementation<TValue>> behind the scenes, for example. Choose between them based on your requirements. Personally I find that the lookup is usually a better fit than a Dictionary<TKey, List<TValue>>, mostly due to the first two points above.

请注意，作为一个实现细节，具体落实 IGrouping＆LT;，＆GT; 这是用于数值工具的IList＆LT; TValue＆GT; ，这意味着它的效率与 COUNT（），的ElementAt（）等。

Note that as an implementation detail, the concrete implementation of IGrouping<,> which is used for the values implements IList<TValue>, which means that it's efficient to use with Count(), ElementAt() etc.