Question

Here is my point:
here is data class:

class Data
{
public string name; 
public int version;
}

here is data lists:

Ilist<Data> List_old = {new Data{name = "1", version = 1}, new Data{name = "2", version = 1}};
Ilist<Data> List_new = {new Data{name = "1", version = 2}, new Data{name = "3", version = 1}, new Data{name = "2", version = 1}};

As result I need a list of tuples – IList<Tuple<Data, Data>> – first data object is from List_new, second from List_old, taken by criteria – data objects have the same name but – first have greater version that the second OR second is null if there in List_old there is no any data item with the same name from List_new.
Considering that the result should be:

IList<Tuple<Data, Data>> result = { {List_new[0], List_old[0]}, {List_new[1], null}};

could You help with the LINQ code which could perform that?
I blow my brains with this…

Answer 1

If I’ve interpreted your question correctly:

var q = 
    (from n in List_new
    join tmp in List_old on n.name equals tmp.name into g
    from o in g.DefaultIfEmpty()
    where o == null || o.version < n.version
    select new Tuple<Data, Data>(n, o)).ToList();