Asp.net Select 多个字段分组并求和

发布于04月19日

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

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

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 
        });

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.

Asp.net Select 多个字段分组并求和

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