过滤重复了IEnumerable的 [英] Filtering duplicates out of an IEnumerable

问题描述

我有这样的代码：

class MyObj {
    int Id;
    string Name;
    string Location;
}

IEnumerable<MyObj> list;

我想列表转换为这样的字典：

I want to convert list to a dictionary like this:

list.ToDictionary(x => x.Name);

但它告诉我，我有重复键。我怎么能只保留第一项为每个键？

but it tells me I have duplicate keys. How can I keep only the first item for each key?

推荐答案

我想最简单的方法是将GROUP BY键，并采取每个组的第一个元素：

I suppose the easiest way would be to group by key and take the first element of each group:

list.GroupBy(x => x.name).Select(g => g.First()).ToDictionary(x => x.name);

或者，如果你的对象，你可以使用鲜明实施 IEquatable 来者皆它们之间比较：

Or you could use Distinct if your objects implement IEquatable to compare between themselves by key:

// I'll just randomly call your object Person for this example.
class Person : IEquatable<Person> 
{
    public string Name { get; set; }

    public bool Equals(Person other)
    {
        if (other == null)
            return false;

        return Name == other.Name;
    }

    public override bool Equals(object obj)
    {
        return base.Equals(obj as Person);
    }

    public override int GetHashCode()
    {
        return Name.GetHashCode();
    }
}

...

list.Distinct().ToDictionary(x => x.Name);

或者，如果你不想做（也许是因为你通常要比较的平等以不同的方式，所以等于已在使用），你可以做的自定义实现的IEqualityComparer 只是这种情况下：

Or if you don't want to do that (maybe because you normally want to compare for equality in a different way, so Equals is already in use) you could make a custom implementation of IEqualityComparer just for this case:

class PersonComparer : IEqualityComparer<Person>
{
    public bool Equals(Person x, Person y)
    {
        if (x == null)
            return y == null;

        if (y == null)
            return false;

        return x.Name == y.Name;
    }

    public int GetHashCode(Person obj)
    {
        return obj.Name.GetHashCode();
    }
}

...

list.Distinct(new PersonComparer()).ToDictionary(x => x.Name);

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