高级GroupBy

Question

我有一份结构如下的物品清单：

1. Id
2. DateTime
3. Weight

如何用Id和Date of Date字段(即DateTime)对它们进行分组，并拥有该组的总重量？我想要这样的东西：

1. Id
2. Date
3. TotalWeight

Answer 1

如果您想同时使用ID和日期对它们进行分组，可以这样做：

var grp = from x in items
          group by new {x.Id, x.DateTime.Date};

var result = grp.Select(x=>new {item = x.Key, TotalWeight = x.Sum(y=>y.Weight)});

Answer 2

var result = from x in items
             group x by new { x.Id, x.DateTime.Date } into grouping
             select new 
             { 
                 id = grouping.Key.Id, 
                 Date = grouping.Key.Date, 
                 TotalWeight = grouping.Sum(y=>y.Weight)
             };