Does .NET have a way to check if List a contains all items in List b?

Question

I have the following method:

namespace ListHelper
{
    public class ListHelper<T>
    {
        public static bool ContainsAllItems(List<T> a, List<T> b)
        {
            return b.TrueForAll(delegate(T t)
            {
                return a.Contains(t);
            });
        }
    }
}

The purpose of which is to determine if a List contains all the elements of another list. It would appear to me that something like this would be built into .NET already, is that the case and am I duplicating functionality?

Edit: My apologies for not stating up front that I'm using this code on Mono version 2.4.2.

See also https://stackoverflow.com/questions/332973/check-whether-an-array-is-a-subset-of-another — Colonel Panic, Jan 05 '16 at 16:41
Your algorithm is quadratic O(nm). If the lists are sorted, testing if one is a subset of another should be possible in O(n+m) time. — Colonel Panic, Jan 05 '16 at 16:49

score 205 · Accepted Answer · edited Jan 31 '19 at 21:17

205

If you're using .NET 3.5, it's easy:

public class ListHelper<T>
{
    public static bool ContainsAllItems(List<T> a, List<T> b)
    {
        return !b.Except(a).Any();
    }
}

This checks whether there are any elements in b which aren't in a - and then inverts the result.

Note that it would be slightly more conventional to make the method generic rather than the class, and there's no reason to require List<T> instead of IEnumerable<T> - so this would probably be preferred:

public static class LinqExtras // Or whatever
{
    public static bool ContainsAllItems<T>(this IEnumerable<T> a, IEnumerable<T> b)
    {
        return !b.Except(a).Any();
    }
}

edited Jan 31 '19 at 21:17

RMalke

4,048
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answered Oct 05 '09 at 15:06

Jon Skeet

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This is untested, but wouldn't return b.Except(a).Empty(); be much more readable ? – Nils Oct 05 '09 at 15:13
7

Except that Empty() doesn't return a boolean. It returns an IEnumerable with no items. – Peter Stephens Oct 05 '09 at 15:27
This requires Linq right? If so, I don't think that's available in Mono, which is what I'm using at the moment. – Matt Haley Oct 05 '09 at 16:23
2

You can use LINQ to Objects in Mono, I believe... but it would be helpful if you'd state the requirements in the question to start with. Which version of Mono are you using? – Jon Skeet Oct 05 '09 at 16:37
I've just checked the sources for Mono 2.4.2.3, and it definitely includes LINQ to Objects. – Jon Skeet Oct 05 '09 at 16:52
1

If the lists are length n and m, what's the time complexity of this algorithm? – Colonel Panic Jan 05 '16 at 16:50
1

@ColonelPanic: Assuming no hash collisions, O(n+m). – Jon Skeet Jan 05 '16 at 16:52
If two lists are identical, this will return false, because there wouldn't be Any() elements found after the Except() – Bojan Oct 23 '20 at 11:35
@Bojan: No, it will return true, because the expression starts with `!`. See https://dotnetfiddle.net/QdXPy7 for a runnable example. – Jon Skeet Oct 23 '20 at 12:47

score 48 · Answer 2 · edited Sep 26 '16 at 00:44

48

Included in .NET 4: Enumerable.All

public static bool ContainsAll<T>(IEnumerable<T> source, IEnumerable<T> values)
{
    return values.All(value => source.Contains(value));
}

edited Sep 26 '16 at 00:44

orad

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answered Apr 26 '16 at 06:02

Thomas

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score 36 · Answer 3 · edited May 23 '17 at 11:54

36

Just for fun, @JonSkeet's answer as an extension method:

/// <summary>
/// Does a list contain all values of another list?
/// </summary>
/// <remarks>Needs .NET 3.5 or greater.  Source:  https://stackoverflow.com/a/1520664/1037948 </remarks>
/// <typeparam name="T">list value type</typeparam>
/// <param name="containingList">the larger list we're checking in</param>
/// <param name="lookupList">the list to look for in the containing list</param>
/// <returns>true if it has everything</returns>
public static bool ContainsAll<T>(this IEnumerable<T> containingList, IEnumerable<T> lookupList) {
    return ! lookupList.Except(containingList).Any();
}

edited May 23 '17 at 11:54

Community

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answered Oct 26 '12 at 17:58

drzaus

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similarly: Contains Any = `public static bool ContainsAny(this IEnumerable haystack, IEnumerable needle) { return haystack.Intersect(needle).Count() > 0; }`. I tried some quick performance comparisons to `haystack.Count() - 1 >= haystack.Except(needle).Count();` and `Intersect` seemed to do better most of the time. – drzaus May 23 '13 at 16:21
4

sheesh...use `Any()` not `Count() > 0`: `public static bool ContainsAny(this IEnumerable haystack, IEnumerable needle) { return haystack.Intersect(needle).Any(); }` – drzaus Jun 04 '13 at 14:34

BaiaccuTerrestre_BR · Answer 4 · 2022-01-17T18:15:13.223

3

I know a way using LinQ methods. It's a bit weird to read, but works pretty well

var motherList = new List<string> { "Hello", "World", "User };
var sonList = new List<string> { "Hello", "User" };

You want to check if sonList is totally in motherList

To do so:

sonList.All(str => moterList.Any(word => word == str));

// Reading literally, would be like "For each of all items 
// in sonList, test if it's in motherList

Please check it on and see if works there too. Hope it helps ;-)

edited Jan 17 '22 at 18:15

answered Jan 17 '22 at 17:08

BaiaccuTerrestre_BR

39
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This works. But please correct the typo in this line: `bool result = sonList.All(str => motherList.Any(word => word == str));` – Shubhjot Aug 04 '23 at 18:07

score -1 · Answer 5 · edited Oct 07 '15 at 11:21

-1

You could also use another way. Override equals and use this

public bool ContainsAll(List<T> a,List<T> check)
{
   list l = new List<T>(check);
   foreach(T _t in a)
   {
      if(check.Contains(t))
      {
         check.Remove(t);
         if(check.Count == 0)
         {
            return true;
         }
      }
      return false;
   }
}

edited Oct 07 '15 at 11:21

Rohit Vipin Mathews

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answered Jan 26 '14 at 18:54

user3210251

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`list l = new List(check);` I dont think this would compile and if it does, its totally unecessary as `check` is already a list – Rohit Vipin Mathews Oct 07 '15 at 11:22

Does .NET have a way to check if List a contains all items in List b?

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