GROUPBY在lambda表达式 [英] GroupBy in lambda expressions

问题描述

from x in myCollection
    group x by x.Id into y
    select new { 
       Id = y.Key, 
       Quantity = y.Sum(x => x.Quantity)
    };

您会怎么写上面Lambda表达式？我卡上的组到部分。

How would you write the above as a lambda expression? I'm stuck on the group into part.

推荐答案

查询延续（SELECT ... INTO和组...成，但的不的加入...进入）等价于刚分手的查询表达式。所以我喜欢把你的例子为：通过X从X MyCollection中
组X

Query continuations (select...into and group...into, but not join...into) are equivalent to just splitting up the query expression. So I like to think of your example as:

var tmp = from x in myCollection
          group x by x.Id;
var result = from y in tmp
             select new { 
               Id = y.Key, 
               Quantity = y.Sum(x => x.Quantity)
             };

改变那些进入点符号：

Change those into dot notation:

var tmp = myCollection.GroupBy(x => x.Id);
var result = tmp.Select(y => new { 
               Id = y.Key, 
               Quantity = y.Sum(x => x.Quantity)
             });

然后，你可以将它们合并回：

Then you could combine them back:

var tmp = myCollection.GroupBy(x => x.Id)
                      .Select(y => new { 
                                Id = y.Key, 
                                Quantity = y.Sum(x => x.Quantity)
                              });

一旦你制定出C＃编译器与查询表达式是什么，其余的是相对简单的：）

Once you work out what the C# compiler does with query expressions, the rest is relatively straightforward :)

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