Find if listA contains any elements not in listB

Question

I have two lists:

List listA     
List listB

How to check using LINQ if in the listA exists an element w

Answer 1

List has Contains method that return bool. We can use that method in query.

List<int> listA = new List<int>();
List<int> listB = new List<int>();
listA.AddRange(new int[] { 1,2,3,4,5 });
listB.AddRange(new int[] { 3,5,6,7,8 });

var v = from x in listA
        where !listB.Contains(x)
        select x;

foreach (int i in v)
    Console.WriteLine(i);

Answer 2

This piece of code compares two lists both containing a field for a CultureCode like 'en-GB'. This will leave non existing translations in the list. (we needed a dropdown list for not-translated languages for articles)

var compared = supportedLanguages.Where(sl => !existingTranslations.Any(fmt => fmt.CultureCode == sl.Culture)).ToList();

Answer 3

if (listA.Except(listB).Any())

Answer 4

You can do it in a single line

var res = listA.Where(n => !listB.Contains(n));

This is not the fastest way to do it: in case listB is relatively long, this should be faster:

var setB = new HashSet(listB);
var res = listA.Where(n => !setB.Contains(n));

Answer 5

Get the difference of two lists using Any(). The Linq Any() function returns a boolean if a condition is met but you can use it to return the difference of two lists:

var difference = ListA.Where(a => !ListB.Any(b => b.ListItem == a.ListItem)).ToList();

Answer 6

listA.Any(_ => listB.Contains(_))

:)