Linq - How To Check Intersecting Objects Between Lists

Question

I have two list of objects. For e.g. say the objects are like below

class A
{
    int ID;
    int Value;
}

class B
{
    int ID;
    int Value;
}

I have two list of above objects like List<A> AList and List<B> BList. I want to find if any object in List<B> has matching Value from List<A>.

For now, what I do like is

foreach(var item in AList)
{
    if(!BList.Any(x => x.Value == item.Value))
    {
        //Handle the error message
    }
}

Is there any better way to do it by Linq?

Use contain . objListB.contains(objListA); – CodeConstruct Mar 25 '17 at 16:14 — CodeConstruct, Mar 25 '17 at 16:14

score 1 · Answer 1 · edited Mar 25 '17 at 13:17

1

Simply:

from a in AList
join b in BList on a.Value equals b.Value
select a

edited Mar 25 '17 at 13:17

ataravati

8,891
9
57
89

answered Mar 25 '17 at 13:08

Arnaud F.

8,252
11
53
102

score 1 · Accepted Answer · answered Mar 25 '17 at 13:21

1

You can do it this way. This will be true if there are any items in BList that have matching values in AList:

BList.Any(b => AList.Select(a => a.Value).Contains(b.Value))

answered Mar 25 '17 at 13:21

ataravati

8,891
9
57
89

score 1 · Answer 3 · answered Mar 25 '17 at 13:37

1

Try this:

BList.Any(b => AList.Any(a => a.Value == b.Value));

answered Mar 25 '17 at 13:37

Abdullah Dibas

1,499
1
9
13

Kerim Emurla · Answer 4 · 2017-03-25T14:42:18.523

This is what I've tried and it seems to work just fine:

    class First
    {
        public int Id { get; set; }
        public int Value { get; set; }
    }

    class Second
    {
        public int Id { get; set; }
        public int Value { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var firstList = new List<First>
            {
                new First { Id = 1, Value = 2 },
                new First { Id = 1, Value = 10 },
                new First { Id = 1, Value = 0 }
            };

            var secondList = new List<Second>
            {
                new Second { Id = 1, Value = 2 },
                new Second { Id = 1, Value = 2 },
                new Second { Id = 1, Value = 4 }
            };

            bool hasCommonValues = firstList.Select(f => f)
                                   .Any(u => secondList.Select(x => x.Value)
                                   .Contains(u.Value));

            Console.WriteLine(hasCommonValues);        
        }
    }

score 1 · Answer 5 · edited May 23 '17 at 12:17

According to your current code, and if you just need to handle error when any item in AList doesn't have a matching item in BList, you can do as follows :

if (AList.Any(a => !BList.Any(b => b.Value == a.Value)))
{
    //Handle error
}

Or if you need to take an action on every item in AList that doesn't have a matching item in BList :

foreach(var item in AList.Where(a => !BList.Any(b => b.Value == a.Value)))
{
    //Handle error for current `item`
}

Anyways, the reason to prefer LINQ over conventional foreach loop is usually more for its readability (shorter, cleaner, easier to maintain, etc.) rather than performance. For reference : Is a LINQ statement faster than a 'foreach' loop?

Linq - How To Check Intersecting Objects Between Lists

5 Answers5