get common elements in lists in C#
Use Intersect
:
var commonElements = list1.Intersect(list2).ToList();
The extra 1 means you can't use Intersect
because it returns a set.
Here's some code that does what you need:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
var grouped1 =
from n in list1
group n by n
into g
select new {g.Key, Count = g.Count()};
var grouped2 =
from n in list2
group n by n
into g
select new {g.Key, Count = g.Count()};
var joined =
from b in grouped2
join a in grouped1 on b.Key equals a.Key
select new {b.Key, Count = Math.Min(b.Count, a.Count)};
var result = joined.SelectMany(a => Enumerable.Repeat(a.Key, a.Count));
CollectionAssert.AreEquivalent(new[] {1, 1, 2}, result);
This works nicely:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
var lookup1 = list1.ToLookup(x => x);
var lookup2 = list2.ToLookup(x => x);
var results = lookup1.SelectMany(l1s => lookup2[l1s.Key].Zip(l1s, (l2, l1) => l1));