多重分组和求和的LINQ查询

Question

我有一个产品销售表，长这样：

saleDate     prod        qty
10/22/09     soap        10
09/22/09     pills       05
09/25/09     soap        06
09/25/09     pills       15

我需要对每个月的数值进行求和，使得最终的表格看起来像这样：

saleDate     prod        qty
10/09        soap        10
09/09        soap        06
09/09        pills       20

我能用LINQ做到这个吗？

- Luiscencio

Answer 1

var products = new[] {
    new {SaleDate = new DateTime(2009,10,22), Product = "Soap", Quantity = 10},
    new {SaleDate = new DateTime(2009,09,22), Product = "Pills", Quantity = 5},
    new {SaleDate = new DateTime(2009,09,25), Product = "Soap", Quantity = 6},
    new {SaleDate = new DateTime(2009,09,25), Product = "Pills", Quantity = 15}
};

var summary = from p in products
              let k = new
              {
                   //try this if you need a date field 
                   //   p.SaleDate.Date.AddDays(-1 *p.SaleDate.Day - 1)
                  Month = p.SaleDate.ToString("MM/yy"),
                  Product = p.Product
              }
              group p by k into t
              select new
              {
                  Month = t.Key.Month,
                  Product = t.Key.Product,
                  Qty = t.Sum(p => p.Quantity)
              };

foreach (var item in summary)
    Console.WriteLine(item);

//{ Month = 10/09, Product = Soap, Qty = 10 }
//{ Month = 09/09, Product = Pills, Qty = 20 }
//{ Month = 09/09, Product = Soap, Qty = 6 }

- Matthew Whited

---

哇，这个LINQ的东西超出了我的理解范围...我会试试这个然后回复你。谢谢 - Luiscencio

如果您正在对 SQL 进行此操作，请告诉我它的运行情况。 - Matthew Whited

它运行得相当不错，只需要修改一些细节，我正在使用它来对抗一个数据表对象，稍后我会再试试针对SQL...谢谢=3 - Luiscencio

这是一个非常疯狂的 LINQ 语句，我喜欢它！ - Bill Software Engineer

我之前被推荐使用过这个查询，现在又回来用它了。太棒了，非常感谢。 - Erdinç

Answer 2

var q = from s in sales
       group s by new {saleDate = s.saleDate.ToString("MM/yy"), s.prod} into g
       select new { g.Key.saleDate, g.Key.prod, qty = g.Sum(s => s.qty) };

- manji

Answer 3

class Program
{
    static void Main(string[] args)
    {
        var sales = new List<Sale>();
        sales.Add(new Sale() { Product = "soap", saleDate = new DateTime(2009, 10, 22), Quantity = 10});
        sales.Add(new Sale() { Product = "soap", saleDate = new DateTime(2009, 9,22), Quantity = 6});
        sales.Add(new Sale() { Product = "pills", saleDate = new DateTime(2009,9,25), Quantity = 15});
        sales.Add(new Sale() { Product = "pills", saleDate = new DateTime(2009,9,25), Quantity = 5});

        var q = from s in sales
                group s by new { s.Product, s.saleDate.Month, s.saleDate.Year } into g
                select new {Month = String.Format("{0:MM/yy}", new DateTime(g.Key.Year, g.Key.Month, 1)), product = g.Key.Product, quantity = g.Sum(o=>o.Quantity)};


    }
}

class Sale
{
    public DateTime saleDate { get; set; }
    public int Quantity { get; set; }
    public string Product { get; set; }
}

- Jason Punyon

Answer 4

当然可以。

它将呈现为以下这种形式：

var GroupedSales = 
      from p in products 
      group p by p.saleDate.Month into g 
      select new { saleMonth = g.saleDate.Month, QtySold = g.Sum(p => p.qty) }; 

请参考：http://msdn.microsoft.com/en-us/vcsharp/aa336747.aspx#sumGrouped

另外，请注意我是在假设你的数据集只有2009年的数据的情况下进行操作的。如果你想按月/年分组，可以使用saleDate.ToString("yyyyMM")而不是saleDate.Month。

- Cam Soper

---

你也可以使用 (saleDate.Year*12+saleDate.Month)。 - Sam Harwell