c# - 检查 List 元素是否包含具有特定属性值的项目

Question

public class Item
{
    public List<int> val { get; set; }
    public double support { get; set; }
}

我声明变量:

List<Item> t = new List<Item>();
t.Add(new Item(){val = new List<int>(){1,2,3};support=.1);
var b = new Item();
b.val = t[0].val;
b.support=t[0].support;
t.Contain(b) // return false???

我正在尝试使用 linq

t.Any(a=>a.val==b.val) // I'm get error Expression cannot contain lambda expressions

Answer 1

我想到了 3 种可能性:

你可以实现 IEquatable<T> :

public class Item: IEquatable<Item>
{
    public List<int> val { get; set; }
    public double support { get; set; }

    public bool Equals(Item other)
    {
        return
            this.support == other.support &&
            this.val.SequenceEqual(other.val);
    }
}

现在t.Contains(b)将返回 true。

---

如果您无法修改 Item类你可以写一个自定义 EqualityComparer :

public class ItemEqualityComparer : IEqualityComparer<Item>
{
    private ItemEqualityComparer()
    {
    }

    public static IEqualityComparer<Item> Instance
    {
        get
        {
            return new ItemEqualityComparer();
        }
    }

    public bool Equals(Item x, Item y)
    {
        return
            x.support == y.support &&
            x.val.SequenceEqual(y.val);
    }

    public int GetHashCode(Item obj)
    {
        int hash = 27;
        hash += (13 * hash) + obj.support.GetHashCode();
        foreach (var item in obj.val)
        {
            hash += (13 * hash) + item.GetHashCode();
        }
        return hash;
    }
}

然后 t.Contains(b)还将返回 true .

---

或者，如果您更喜欢天真地做:

List<Item> t = new List<Item>();
t.Add(new Item { val = new List<int>(){1,2,3}, support=.1 });

var b = new Item();
b.val = t[0].val;
b.support = t[0].support;

bool equals = t.All(item => item.support == b.support && item.val.SequenceEqual(b.val));
Console.WriteLine(equals);