c# - 在 C# 中查找列表中的多个重复值

Question

那么，假设我有一份汽车 list 。列表中的每个项目都有一个品牌和一个颜色属性。我想找出每个品牌有多少相同颜色的品牌，然后打印该信息。该列表将由用户输入填充。我无法确定列表中将包含哪些确切值。

例子:

class Car
    {
        public string brand;
        public string color;
    }

    private void DoSomething()
    {
        List<Car> cars = new List<Car>();
        cars.Add(new Car { brand = "Toyota", color = "blue" });
        cars.Add(new Car { brand = "Toyota", color = "red" });
        cars.Add(new Car { brand = "Toyota", color = "blue" });
        cars.Add(new Car { brand = "Audi", color = "red" });
        cars.Add(new Car { brand = "Audi", color = "red" });
        cars.Add(new Car { brand = "Audi", color = "blue" });

        // Find out for each brand how many there are of the same color, and then print that info
        // Example output: Toyota: 2 blue, 1 red
        //                 Audi:   2 red, 1 blue
    }

我花了很长时间寻找一种方法来做到这一点。我所能弄清楚的是如何获得列表中某个项目的出现次数。

如果我的问题不清楚，请告诉我，我会尝试解释更多。

Answer 1

一些 linq 应该这样做:

var result = cars.GroupBy(x => new { x.brand, x.color })
    .Select(x => new { 
        Brand = x.Key.brand, 
        Color = x.Key.color, 
        Count = x.Count() 
    });