c# linq扩展组并按季度选择数据，其中缺少月份

Question

我有由日期和总数组成的数据。我需要按季度计算销售总额。输出按季度返回销售总额数组，结果为Q1的销售和，结果1为Q2的销售和等等。

例如，输入'sales'：

/// {} => { 0, 0, 0, 0}
/// {(1/1/2010, 10), (2/2/2010, 10), (3/3/2010, 10)} => { 30, 0, 0, 0 }
/// {(1/1/2010, 10), (4/4/2010, 10), (10/10/2010, 10)} => { 10, 10, 0, 10 }

我想出了如何分组的办法，但对失踪的宿舍有个问题。

sales.GroupBy(item => ((item.Item1.Date.Month - 1) / 3))
     .Select(x => new { Quarter = x.Key, Sum = x.Sum(item => item.Item2) })

一个solution是不错的，但我不能处理好我的情况

Answer 1

因为您的数据不一定包含所有季度，所以您应该将其left join到所有季度的集合中。要创建这样的使用Enumerable.Range

var groupedSales = sales.GroupBy(item => ((item.Date.Month - 1) / 3))
                        .Select(x => new { Quarter = x.Key, 
                                           Sum = x.Sum(item => item.Amount) });

var result = (from quarter in Enumerable.Range(0, 4)
              join sale in groupedSales on quarter equals sale.Quarter into grouping
              from sale in grouping.DefaultIfEmpty()
              select new { Quarter = quarter, Sum = sale?.Sum ?? 0 }).ToList();

一些测试数据：

List<dynamic> sales = new List<dynamic>
{
   new { Date = new DateTime(2010,1,1), Amount = 10 },
   new { Date = new DateTime(2010,2,2), Amount = 10 },
   new { Date = new DateTime(2010,3,3), Amount = 10 },
   new { Date = new DateTime(2010,4,4), Amount = 10 },
   new { Date = new DateTime(2010,5,5), Amount = 10 },
   new { Date = new DateTime(2010,6,6), Amount = 10 },
};