Question

I have a List<List<int>>. I would like to convert it into a List<int> where each int is unique. I was wondering if anyone had an elegant solution to this using LINQ.

I would like to be able to use the Union method but it creates a new List<> everytime. So I’d like to avoid doing something like this:

List<int> allInts = new List<int>();  foreach(List<int> list in listOfLists)    allInts = new List<int>(allInts.Union(list)); 

Any suggestions?

Thanks!

Answer 1

List<List<int>> l = new List<List<int>>();  l.Add(new List<int> { 1, 2, 3, 4, 5, 6}); l.Add(new List<int> { 4, 5, 6, 7, 8, 9 }); l.Add(new List<int> { 8, 9, 10, 11, 12, 13 });  var result = (from e in l               from e2 in e               select e2).Distinct(); 

Update 09.2013

But these days I would actually write it as

var result2 = l.SelectMany(i => i).Distinct();