Find if listA contains any elements not in listB

Question

I have two lists:

List<int> listA     
List<int> listB

How to check using LINQ if in the listA exists an element wchich deosn't exists in the listB ? I can use the foreach loop but I'm wondering if I can do this using LINQ

score 102 · Accepted Answer · answered Mar 01 '12 at 21:51

102

listA.Except(listB) will give you all of the items in listA that are not in listB

answered Mar 01 '12 at 21:51

cadrell0

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Yes, it will do this. But as this is a set based operation it's worth remembering that the resulting list will also remove duplicates present in either ListA or ListB. – Holf Jan 27 '16 at 15:56

score 38 · Answer 2 · answered Mar 01 '12 at 21:52

38

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

answered Mar 01 '12 at 21:52

SLaks

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score 17 · Answer 3 · answered Mar 01 '12 at 21:53

17

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

:)

answered Mar 01 '12 at 21:53

the_joric

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This is best anwser, because solutions provided by @cadrell0 and SLaks will only check if A contains all elements of B but not if B has any more elements that don't match A. This solution is valid for example below. A: [0,1,2,3]; B: [0,1,2,3,4] `listA.Except(listB).Any() == false` `listA.Any(_ => listB.Contains(_)) == true` – Tomasz Juszczak Jan 02 '17 at 13:23
2

@TomaszJuszczak True, but the question specifically asked only if A contains anything not in B - i.e. it **should** evaluate to false if B contains something not in A provided A doesn't contain something not in B. So this answer is incorrect. (Yes, I misunderstood the question when I first read.) – Ian Goldby Mar 17 '17 at 10:03
As you're actually using the value from Any, you shouldn't use discard ( _ ) because it means (to dev and compiler) that you don't care about value – cdie Jan 22 '21 at 10:03

score 9 · Answer 4 · answered Mar 01 '12 at 21:52

9

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));

answered Mar 01 '12 at 21:52

Sergey Kalinichenko

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score 5 · Answer 5 · answered Sep 11 '19 at 13:17

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();

score 3 · Answer 6 · answered Mar 01 '12 at 21:55

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);

score 2 · Answer 7 · answered Nov 13 '17 at 10:01

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();

Find if listA contains any elements not in listB

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