Question

我有List<List<ProductFilter>>

public class ProductFilter
{
    public int Id { get; set; }
    public int FilterValueId { get; set; }
    public int ProductId { get; set; }
    public int? FilterId { get; set; }
    public string FilterValue { get; set; }
    public string FilterName { get; set; }
}

我想要Intersect之前的ProductId并返回ProductFilter。有可能吗我尝试：

var intersection = groupList
  .Aggregate((previousList, nextList) => previousList
     .Select(x => x.ProductId)
     .Intersect(nextList.Select(x => x.ProductId))
  .ToList());

但是它给了我错误，因为返回int：

无法隐式转换类型'System.Collections.Generic.List<int>' 到“ System.Collections.Generic.List<ProductFilter>”

Answer 1

您正在收到上述错误，因为对于Aggregate即List<ProductFilter>的这种特定重载，累加器函数将返回与源中元素相同的类型。而不是List<int>。

要产生IEnumerable<int>作为结果，请先将项目投影到IEnumerable<int>，然后调用Aggregate：

groupList.Select(p => p.Select(e => e.ProductId))
         .Aggregate((previousList, nextList) => previousList.Intersect(nextList));

Answer 2

为此，您必须使用Intersect的重载，该重载接受IEqualityComparer<>

class ProductFilterProductIdEqualityComparer : IEqualityComparer<ProductFilter>
{
    public bool Equals(ProductFilter x, ProductFilter y)
    {
        if (ReferenceEquals(x, y))
            return true;
        if (ReferenceEquals(x, null))
            return false;
        if (ReferenceEquals(y, null))
            return false;
        return x.ProductId == y.ProductId;
    }

    public int GetHashCode(ProductFilter obj) => obj.ProductId;
}

var productFilterProductIdEqualityComparer = new ProductFilterProductIdEqualityComparer();
var intersection = groupList
    .Aggregate((previousList, nextList) => 
        previousList.Intersect(nextList, productFilterProductIdEqualityComparer)
    .ToList());

注意：请记住，当两个ProductFilter具有相同的ProductId但在其他属性上不同时，您只会在intersection中得到第一个属性< / p>

通过一个属性相交多个列表

2 个答案: