如何在 Linq 的单个查询中使用 Distinct() 和 Sum()

Question

这里我有 2 列，例如编号，数量。我想在 LINQ 中获取 Distinct Id 及其数量总和。我试过这样

var r = list.Where(some operation)
            .Select(x => x.Id)
            .Distinct()
            .Select(x => (int?)x.Quantity))
            .Sum();

这里 x.Quantity 我遇到了错误..我该如何解决.. 请提出您的建议

Answer 1

按 Id 分组。比你能做的：

.GroupBy(x => x.Id)
.Select(x => new { x.Key, x.Sum(y => (int?)y.Quantity) });

Answer 2

如果我假设 Id 是 int 并且 Quantity 是 string，那么您也可以使用聚合。下面是一个例子：

class TestClass
{
    public int I { get; set; }
    public string S { get; set; }
}

class Program
    {
        static void Main()
        {
            var myclass = new TestClass[]
            {
                new TestClass {I = 1, S = "1"}, new TestClass { I = 1, S = "11" }, new TestClass { I = 1, S = "111" },
                new TestClass {I = 2, S = "2"},new TestClass {I = 2, S = "222"},new TestClass {I = 2, S = "2"},
                new TestClass {I = 3, S = "3"},new TestClass {I = 3, S = "333"},new TestClass {I = 3, S = "33"},
                new TestClass {I = 4, S = "44"},new TestClass {I = 4, S = "4"},
                new TestClass {I = 5, S = "5"}
            };

            var filteredObject = myclass.GroupBy(x => x.I).Select(y => new
            {
                I = y.Key,
                S = y.Select(z => z.S).Aggregate((a, b) => (Convert.ToInt32(a) + Convert.ToInt32(b)).ToString())
            });

            filteredObject.ToList().ForEach(x => Console.WriteLine(x.I + "    " + x.S));
        }

    }

结果如下：

1 123

2226

3 369

4 48

5 5

按任意键继续。 . .

希望对您有所帮助。

如何在 Linq 的单个查询中使用 Distinct() 和 Sum()

How to Use Distinct() and Sum() in Single Query in Linq

linq

c#-4.0