选择多个字段分组并求和 [英] Select multiple fields group by and sum

问题描述

我想用linq(对象列表)进行查询，但我真的不知道该怎么做，我可以进行分组和求和，但不能选择其余字段. 示例:

I want to do a query with linq (list of objects) and I really don't know how to do it, I can do the group and the sum but can't select rest of the fields. Example:

ID  Value     Name   Category
1   5         Name1  Category1  
1   7         Name1  Category1
2   1         Name2  Category2
3   6         Name3  Category3
3   2         Name3  Category3

我想按ID分组，按值求和，并返回所有类似的字段.

I want to group by ID, SUM by Value and return all fields like this.

ID  Value     Name   Category
1   12        Name1  Category1  
2   1         Name2  Category2
3   8         Name3  Category3

推荐答案

已更新: 如果要避免对所有字段进行分组，则可以仅按Id进行分组:

Updated : If you're trying to avoid grouping for all the fields, you can group just by Id:

data.GroupBy(d => d.Id)
    .Select(
        g => new
        {
            Key = g.Key,
            Value = g.Sum(s => s.Value),
            Name = g.First().Name,
            Category = g.First().Category 
        });

但是此代码假定对于每个Id，都应用相同的Name和Category.如果是这样，您应该考虑按照@Aron的建议进行规范化.这意味着将Id和Value保留在一个类中，并将Name，Category(以及对于相同的Id而言，其他任何字段都相同)移至另一类，同时还具有Id以供参考.规范化过程减少了数据冗余和依赖性.

But this code assumes that for each Id, the same Name and Category apply. If so, you should consider normalizing as @Aron suggests. It would imply keeping Id and Value in one class and moving Name, Category (and whichever other fields would be the same for the same Id) to another class, while also having the Id for reference. The normalization process reduces data redundancy and dependency.

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