在c#列表中搜索重复元素

Question

我需要遍历一个列表，并计算给定此模型的所有具有相同id的元素:

public class Product
{
public int ProductId { get; set; }
public string ProductName { get; set; }
}

我想检查列表中所有重复的元素，并将计数存储在一个变量中:

List<Product> productList = new()
{
new Product { ProductName = "item1", ProductId = 1},
new Product { ProductName = "item2", ProductId = 1},
new Product { ProductName = "item3", ProductId = 2},
new Product { ProductName = "item4", ProductId = 2},
new Product { ProductName = "item5", ProductId = 3},
new Product { ProductName = "item6", ProductId = 1}
};

在上面的例子中，结果应该是这样的:

int someProduct1 = 3;
int someProduct2 = 2;
int someProduct3 = 1;

我怎样才能做到那样呢?

Answer 1

try this

var query = productList
.GroupBy(c => c.ProductId)
.Select(o => new 
{
ProductId = o.Key,
Count = o.Count()
});

或只是重复

var query = productList
.GroupBy(c => c.ProductId)
.Select(o => new 
{
ProductId = o.Key,
Count = o.Count()
})
.OrderByDescending (o => o.Count )
.Where(p => p.Count>1);

输出

productId Count
1      3
2      2