如何将 linq 结果转换为 HashSet 或 HashedSet [英] How to convert linq results to HashSet or HashedSet

问题描述

我有一个 ISet 类的属性.我正在尝试将 linq 查询的结果获取到该属性中，但不知道该怎么做.

I have a property on a class that is an ISet. I'm trying to get the results of a linq query into that property, but can't figure out how to do so.

基本上，寻找这个的最后一部分:

Basically, looking for the last part of this:

ISet<T> foo = new HashedSet<T>();
foo = (from x in bar.Items select x).SOMETHING;

也可以这样做:

HashSet<T> foo = new HashSet<T>();
foo = (from x in bar.Items select x).SOMETHING;

推荐答案

我不认为有任何内置的东西可以做到这一点......但编写扩展方法真的很容易:

I don't think there's anything built in which does this... but it's really easy to write an extension method:

public static class Extensions
{
    public static HashSet<T> ToHashSet<T>(
        this IEnumerable<T> source,
        IEqualityComparer<T> comparer = null)
    {
        return new HashSet<T>(source, comparer);
    }
}

请注意，这里确实需要一个扩展方法(或至少是某种形式的通用方法)，因为您可能无法明确表达 T 的类型:

Note that you really do want an extension method (or at least a generic method of some form) here, because you may not be able to express the type of T explicitly:

var query = from i in Enumerable.Range(0, 10)
            select new { i, j = i + 1 };
var resultSet = query.ToHashSet();

您不能通过显式调用 HashSet 构造函数来做到这一点.我们依靠泛型方法的类型推断来为我们做这件事.

You can't do that with an explicit call to the HashSet<T> constructor. We're relying on type inference for generic methods to do it for us.

现在您可以选择将其命名为 ToSet 并返回 ISet - 但我会坚持使用 ToHashSet 和具体类型.这与标准 LINQ 运算符(ToDictionary、ToList)一致，并允许未来扩展(例如 ToSortedSet).您可能还想提供指定要使用的比较的重载.

Now you could choose to name it ToSet and return ISet<T> - but I'd stick with ToHashSet and the concrete type. This is consistent with the standard LINQ operators (ToDictionary, ToList) and allows for future expansion (e.g. ToSortedSet). You may also want to provide an overload specifying the comparison to use.

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