C# 使用 LINQ 选择 Dictionary<T1, T2>
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Select a Dictionary<T1, T2> with LINQ
提问by Rich
I have used the "select" keyword and extension method to return an IEnumerable<T>with LINQ, but I have a need to return a generic Dictionary<T1, T2>and can't figure it out. The example I learned this from used something in a form similar to the following:
我已经使用“select”关键字和扩展方法来返回一个IEnumerable<T>with LINQ，但是我需要返回一个泛型Dictionary<T1, T2>并且无法弄清楚。我从中学到的示例使用了类似于以下形式的内容：
IEnumerable<T> coll = from x in y
select new SomeClass{ prop1 = value1, prop2 = value2 };
I've also done the same thing with extension methods. I assumed that since the items in a Dictionary<T1, T2>can be iterated as KeyValuePair<T1, T2>that I could just replace "SomeClass" in the above example with "new KeyValuePair<T1, T2> { ...", but that didn't work (Key and Value were marked as readonly, so I could not compile this code).
我也对扩展方法做了同样的事情。我假设因为 a 中的项目 Dictionary<T1, T2>可以迭代，KeyValuePair<T1, T2>因为我可以用“”替换上面例子中的“SomeClass new KeyValuePair<T1, T2> { ...”，但这不起作用（键和值被标记为只读，所以我无法编译这段代码）。
Is this possible, or do I need to do this in multiple steps?
这是可能的，还是我需要分多个步骤执行此操作？
Thanks.
谢谢。
采纳答案by Quintin Robinson
The extensions methods also provide a ToDictionaryextension. It is fairly simple to use, the general usage is passing a lambda selector for the key and getting the object as the value, but you can pass a lambda selector for both key and value.
扩展方法还提供了ToDictionary扩展。它使用起来相当简单，一般用法是为键传递一个 lambda 选择器并将对象作为值，但您可以为键和值传递一个 lambda 选择器。
class SomeObject
{
public int ID { get; set; }
public string Name { get; set; }
}
SomeObject[] objects = new SomeObject[]
{
new SomeObject { ID = 1, Name = "Hello" },
new SomeObject { ID = 2, Name = "World" }
};
Dictionary<int, string> objectDictionary = objects.ToDictionary(o => o.ID, o => o.Name);
Then objectDictionary[1]Would contain the value "Hello"
然后objectDictionary[1]将包含值“Hello”
回答by albertein
var dictionary = (from x in y
select new SomeClass
{
prop1 = value1,
prop2 = value2
}
).ToDictionary(item => item.prop1);
That's assuming that SomeClass.prop1is the desired Keyfor the dictionary.
那是假设这SomeClass.prop1是Key字典所需的。
回答by Antoine Meltzheim
A collection of KeyValuePairis even more explicit, and executes very well.
的集合KeyValuePair更加明确，并且执行得非常好。
Dictionary<int, string> dictionary = objects
.Select(x=> new KeyValuePair<int, string>(x.Id, x.Name))
.ToDictionary(x=>x.Key, x=>x.Value);
