join unknown number of lists in linq

Question

I have a situation where I have generated a number of lists which contain integer values. However, the number of these lists is only known at runtime, and i

Answer 1

I assume that you have a List> that holds a variable number of List.

You can intersect the first list with the second list

var intersection = listOfLists[0].Intersect(listOfLists[1]);

and then intersect the result with the third list

intersection = intersection.Intersect(listOfLists[2]);

and so on until intersection holds the intersection of all lists.

intersection = intersection.Intersect(listOfLists[listOfLists.Count - 1]);

Using a for loop:

IEnumerable intersection = listOfLists[0];

for (int i = 1; i < listOfLists.Count; i++)
{
    intersection = intersection.Intersect(listOfLists[i]);
}

Using a foreach loop (as shown by @lazyberezovsky):

IEnumerable intersection = listOfLists.First();

foreach (List list in listOfLists.Skip(1))
{
    intersection = intersection.Intersect(list);
}

Using Enumerable.Aggregate:

var intersection = listOfLists.Aggregate(Enumerable.Intersect);

---

If order is not important, then you can also use a HashSet that you fill with the first list and intersect with with the remaining lists (as shown by @Servy).

var intersection = new HashSet(listOfLists.First());

foreach (List list in listOfLists.Skip(1))
{
    intersection.IntersectWith(list);
}