Group nested list with linq

Question

I have a nested list of objects. That I need to group by identifierA and Sum its numeric properties, nested list shall group respectively:

public class TypeA
{
    public String identifierA{ get; set; }
    public Int32 number { get; set; }
    public List<TypeB> nestedList { get; set; }
}
public class TypeB
{
    public String identifierB { get; set; }
    public Int32 otherNumber { get; set; }
}

So I'm expecting something like this:

var List<TypeA> groupedList = (from a in TypeAList
                               group a by a.identifierA
                               into groupedData
                               select new TypeA
                               {
                                   identifierA = groupedData.Key,
                                   number = groupedData.Sum(g => g.number ),
                                   nestedList = //HOW TO GROUP NESTED PART?
                               }).ToList();

Solution 1

I think that this will resolve your issue.

List<TypeA> list = TypeAList
    .GroupBy(a => a.identifierA)
    .Select(
        g =>
        new TypeA
            {
                identifierA = g.Key,
                number = g.Sum(n => n.number),
                nestedList =
                    g.SelectMany(l => l.nestedList)
                    .GroupBy(b => b.identifierB)
                    .Select(
                        gg =>
                        new TypeB
                            {
                                identifierB = gg.Key,
                                otherNumber = gg.Sum(b => b.otherNumber)
                            }).ToList()
            }).ToList();

Solution 2

SelectMany takes an IEnumerable<SomethingWithAnIEnumerable> and flattens all the SomethingWithAnIEnumerable's selected IEnumerables into a single IEnumerable:

nestedList = groupedData.SelectMany(pa => pa.nestedList).ToList()

Solution 3

use SelectMany

if you want to group the list into one use

nestedList = groupedData.SelectMany(d=>d.nestedList)

and if you want Sum of that list, use

nestedList = groupedData.SelectMany(d=>d.nestedList).Sum(o=>o.otherNumber)

Comments

[sloth]

I think the Sum part is wrong here. I admit that the question is not exactly clear since the OP said HOW TO SUM/GROUP NESTED PART?, but TypeA.nestedList is of type List<TypeB> and not int.

[Sergej Popov]

Yes, that's the one, Thanks!!