汇总清单 <T> 列表中每个项目的属性 <T>

Question

Please refer to ff. codes:

MainObj:

public class MainObj {
    public string Name { get; set; }
    public int SomeProperty { get; set; }
    public List<SubObj> Subojects { get; set; }
}

SubObj:

public class SubObj {
    public string Description { get; set; }
    public decimal Value { get; set; }
}

QUESTION: I have a List<MainObj> . Each item has equal number of SubObj . How do I sum the values of each SubObj from MainObj A which corresponds to the same index as the SubObj in the other MainObj in the list.

To illustrate further:

Results:

{
    Name: "something....",
    Value: SUM(MainObj_A.SubObj[0], MainObj_B.SubObj[0] .... MainObj_n.SubObj[0]
},
{
    Name: "don't really care...."
    Value: SUM(MainObj_A.SubObj[1], MainObj_B.SubObj[1] .... MainObj_n.SubObj[1]
},
{
    Name: "don't really care...."
    Value: SUM(MainObj_A.SubObj[2], MainObj_B.SubObj[2] .... MainObj_n.SubObj[2]
}
.... so on and so forth

I know I can loop thru each item in MainObj then perform the sum but I was hoping that there is a simpler way using Linq .

Sorry if I can't put the right words for my question. I hope the illustrations helped.

Every help would be much appreciated. CHEERS!

Answer 1

As I understand the question you look for something like this:

var results = list.Select((m, i) => new 
          {
             m.Name, 
             Value = list.Sum(t => t.SubObj[i].Value)
          }).ToList();

This creates a list of an anonymous type containing the name of each main object and the sum of all subobject values with the same index as the main object.

---

It's not clear from your question, but if you want to sum all subojects (not only as many as there are main objects), you can do it like this:

var results = Enumerable.Range(0, list[0].SubObj.Count)
                        .Select(i => list.Sum(m => m.SubObj[i].Value)).ToList();

This gives you a list of the sums (without names, as your examples suggest that you "don't really care" about any names).

Answer 2

I would extend solution of Rene, to sum over all subitems:

var result = list.First().Subojects.Select((m, i) => new
{
    Name = i.ToString(),
    Value = list.Sum(t => t.Subojects[i].Value)
}).ToList();

i have used it with this values:

var list = new List<MainObj>
{
    new MainObj { Name = "A", Subojects = new List<SubObj>{new SubObj{ Value = 1}, new SubObj{ Value = 2}, new SubObj{ Value = 3}}},
    new MainObj { Name = "B", Subojects = new List<SubObj>{new SubObj{ Value = 1}, new SubObj{ Value = 2}, new SubObj{ Value = 3}}}
};

And result is:

0:2
1:4
2:6

Answer 3

For flexibility and slightly boosted performance, I'd prefer a mixed LINQ-sql way as shown in my answer below.

var result = from x in list
             where x...
             group x by x.SomeProperty 
             into item
             select new {
             Id = item.Key,
             Name = item.Name,
             Value = item.SubObj.Sum(i => i.Value) 
             };