Find the intersection of two lists in linq?

Question

I have list of int A,B. i like to do the following step in linq

list c = new List();

for (int i = 0; i < a.count; i++)
{
    for (i         


        

Answer 1

You can use Intersect:

var a = new List<int>();
var b = new List<int>();

var c = a.Intersect(b);

Answer 2

Produce a list c containing all elements that are present in both lists a and b:

List<int> c = a.Intersect(b).ToList();

Answer 3

You could use the Intersect method:

var c = a.Intersect(b);

This return all values both in a and b. However, position of the item in the list isn't taken into account.

Answer 4

The LINQ equivalent of your code is:

var c = from i in Enumerable.Range(0, a.Count)
        from j in Enumerable.Range(0, b.Count)
        where a[i] == b[j]
        select a[i];

var cList = c.ToList();

But it's much nicer to do:

var c = from aItem in a 
        join bItem in b on aItem equals bItem
        select aItem;

var cList = c.ToList();

But this doesn't filter duplicates. To filter duplicates completely, you can do:

var cList = a.Intersect(b).ToList();

If you want duplicates to show up as many times as they do in b, for example:

var aSet = new HashSet<int>(a);
var cList = b.Where(aSet.Contains)
             .ToList(); 

Answer 5

As Chris mentions in his comment on the original question, the sample code provided will return duplicates in list c (see his comment for details). Intersect will only return distinct values. To duplicate the behavior of the original sample code, try this:

var c = (from value in a
         where b.Contains(a)
         select a);

Answer 6

This is my version of intersection:

var a = new List<int>();
var b = new List<int>();

// intersection
var c = a.Where(x => b.Any(y => x == y)).ToList();