Question

Say I have a simple address class like below:

public class Address
{
    public int AddressId { get; set; }
    public List<int> NodeIds { get; set; }
}

and have populated a list of addresses like below:

List<Address> listOfAddresses = new List<Address> 
{
    new Address {AddressId=1, NodeIds=new List<int>{1}},
    new Address {AddressId=2, NodeIds=new List<int>{2}},
    new Address {AddressId=3, NodeIds=new List<int>{3}},
    new Address {AddressId=1, NodeIds=new List<int>{4}},
    new Address {AddressId=1, NodeIds=new List<int>{5}}
}

and I want to group by on AddressIds so the result list will have NodeIds that are essentially rolled up in case of duplicates like below:

listOfAddressesWithoutDupes = 
AddressId=1, NodeIds=List<int>{1,4,5},
AddressId=2, NodeIds=List<int>{2}},
AddressId=3, NodeIds=new List<int>{3}

so basically I am looking at a groupby function(or something else) that will get me above
result

List<Address> listOfFilteredAddresses = listOfAddresses.GroupBy(x=>x.AddressId).Select(y=>new Address{AddressId=y.Key, NodeIds=?});

Thanks in advance..

Answer 1

You are almost there:

List<Address> listOfFilteredAddresses =
    listOfAddresses
    .GroupBy(x=>x.AddressId)
    .Select(y=>new Address{
        AddressId=y.Key
    ,   NodeIds=y.SelectMany(x=>x. NodeIds).ToList()
    });

This assumes that NodeIds in the Address are unique; if they are not, add Distinct() after SelectMany.