分組和計數清單項目清單

Question

考慮以下內容：

public class Board
{
    public List<Component> Components { get; set; }
}

public class Component
{
    public int Id { get; set; }
    public string Name { get; set; }
}



var data = new[]{   

    new Board{ 
        Components = new List<Component> {
            new Component{Id = 1, Name= "Item 1"},
            new Component{Id = 2, Name= "Item 2"}
        }
    }, 
    new Board{ 
        Components = new List<Component> {
            new Component{Id = 1, Name= "Item 1"},
            new Component{Id = 3, Name= "Item 3"}
        }
    },      
    new Board{ 
        Components = new List<Component> {
            new Component{Id = 2, Name= "Item 2"},
            new Component{Id = 1, Name= "Item 1"}
        }
    }, 
    new Board{ 
        Components = new List<Component> {
            new Component{Id = 1, Name= "Item 1"},
            new Component{Id = 2, Name= "Item 2"},
            new Component{Id = 3, Name= "Item 3"}
        }
    }, 
};

由此，我需要獲得2個列表：一個包含某個特定組件在所有Board中出現的次數，另一個包含該特定組件在一個Board中一起使用了多少次的列表。

我使用的第一個：

var componentsCount = data.SelectMany(x => x.Components)
               .GroupBy(x => x.Id)
               .Select(x => new { Item = x.First(), Count = x.Count() });

第二個是我的問題，結果應該是這樣的：

[
 {Count = 2, Components = [{ Id = 1, Name = "Item 1"}, { Id = 2, Name = "Item 2"}]}
 {Count = 1, Components = [{ Id = 1, Name = "Item 1"}, { Id = 3, Name = "Item 3"}]}
 {Count = 1, Components = [{ Id = 1, Name = "Item 1"}, { Id = 2, Name = "Item 2"}, { Id = 3, Name = "Item 3"}]} 
]

但是即使開始，我也很難。 LINQ是否有可能，還是我應該求助於foreach和手動比較？ 關於如何實現這一點的任何提示？

Answer 1

您需要根據組件對數據列表進行分組。 您需要實現IEqualityComparer ，該IEqualityComparer會根據Components的Id比較您的列表：

class ComponentListComparer : IEqualityComparer<List<Component>>
{

    public bool Equals(List<Component> x, List<Component> y)
    {
        return x.Select(c => c.Id)
            .OrderBy(c => c)
            .SequenceEqual(y.Select(c => c.Id).OrderBy(c => c));
    }

    public int GetHashCode(List<Component> obj)
    {
        return obj.Select(x => x.Id.GetHashCode() * 23).Sum();
    }

}

然后將其傳遞給GroupBy ：

 var result = data.GroupBy(x => x.Components, new ComponentListComparer())
            .Select(g => new {Count = g.Count(), Components = g.Key})
            .ToList();