.net - 如何使用 linq 按自定义类型分组

Question

我有这个类

public class Item
{
       public Coordinate coordinate { get; set; }
        ...
        ...
}

坐标定义如下:

public class Coordinate
{
        public Coordinate(float latitude, float longitude)
        {
            Latitude = latitude;
            Longitude = longitude;
        }

        public float Latitude { get; private set; }
        public float Longitude { get; private set; }
}

我想要一个这样的 linq 查询:

var grouped = from it in items
              group it by it.Coordinate into grp
              select grp;

As mentioned here by MSDN我认为如果我在我的 Coordinate 类上覆盖 Equals，这是可能的:

Use a named type if you must pass the query variable to another method. Create a special class using auto-implemented properties for the keys, and then override the Equals and GetHashCode methods. You can also use a struct, in which case you do not strictly have to override those methods. For more information see How to: Implement an Immutable Class That Has Auto-Implemented Properties

等于 Coordinate 类的实现:

public override bool Equals(object obj)
{
       var coord = obj as Coordinate;
       if(coord == null) return false;
       return (Latitude == coord.Latitude && Longitude == coord.Longitude);
}

我仍然无法让我的 linq 查询按相似的坐标进行分组，就像我的 失败 测试显示:

[TestMethod]
public void GroupBy_3ItemsWith2DifferentCoordinates_Returns2Groups()
{
    var items = new List<Item>
        {
            new Item {Coordinate = new Coordinate(10, 10)},
            new Item {Coordinate = new Coordinate(10, 10)},
            new Item {Coordinate = new Coordinate(12, 10)},
        };
    var grouped = from it in items
                  group it by it.Coordinate into g
                  select g;
    Assert.AreEqual(2, grouped.Count());
}

GrouBy 方法有一个重载，它将 IEqualityComparer 作为参数，但是否有使用 group 子句的等效项？
我做错了什么吗？？有什么想法吗？

Answer 1

您已经展示了 Equals 实现，但没有展示 GetHashCode。您需要覆盖两者(并以一致的方式)以使分组工作。

示例 GetHashCode 实现:

public override int GetHashCode()
{
    int hash = 23;
    hash = hash * 31 + Latitude.GetHashCode();
    hash = hash * 31 + Longitude.GetHashCode();
    return hash;
}

注意比较 float完全相等的值总是有点风险 - 但我至少希望你的单元测试能够通过，因为它们没有执行任何计算。