c# - IEnumerable.ToLookup

Question

我正在尝试转 IEnumerable<KeyValuePair<string, object>>进入 ILookup<string, object>使用以下代码:

var list = new List<KeyValuePair<string, object>>()
{
    new KeyValuePair<string, object>("London", null),
    new KeyValuePair<string, object>("London", null),
    new KeyValuePair<string, object>("London", null),
    new KeyValuePair<string, object>("Sydney", null)
};

var lookup = list.ToLookup<string, object>(a => a.Key);

但是编译器提示:

Instance argument: cannot convert from 'System.Collections.Generic.List>' to 'System.Collections.Generic.IEnumerable'

和

'System.Collections.Generic.List>' does not contain a definition for 'ToLookup' and the best extension method overload 'System.Linq.Enumerable.ToLookup(System.Collections.Generic.IEnumerable, System.Func)' has some invalid arguments

和

cannot convert from 'lambda expression' to 'System.Func'

我对 lambda 表达式做错了什么？

Answer 1

只需删除 <string, object>对于自动推断的类型:

var lookup = list.ToLookup(a => a.Key);

它真的应该是:

var lookup = list.ToLookup<KeyValuePair<string, object>, string>(a => a.Key);