how to get the difference of two list<> objects ?

Question

i generate a list of an Object called Exceptions :

public class Exceptions
{
    public bool deleted { get; set; }
    public DateTime OriginalDate { get; set; }
    public DateTime StartUtc { get; set; }
    public DateTime EndUtc { get; set; }
    public Int32 NumParticipants { get; set; }
    public String Subject { get; set; }
    public String Location { get; set; }
}

List A got 2 Objects and List B got 3 Objects

I Expect a new List which shows me the difference between the two objects

i tried it with the following function:

var ListC = ListA.Except(ListB).ToList();

i get two objects in ListC which looks exactly like ListA.But i Expected the missing Object from List B.

what am I doing wrong?

Have you provided a custom implementation of `Equals` for your `Exceptions` class? If not, it will do reference comparisons. — adv12, May 28 '14 at 14:57
The missing `Equals`/`GetHashCode` methods aside, if you expect the "missing" object from list B, it should be `ListB.Except(ListA)`, not otherwise. — sloth, May 28 '14 at 14:59
possible duplicate of [Difference between two lists](http://stackoverflow.com/questions/5636438/difference-between-two-lists) — qqbenq, May 28 '14 at 15:00
@ErayGeveci Unsurprisingly. You still have to implement `Equals`/`GetHashCode` or an `IEqualityComparer`. — sloth, May 28 '14 at 15:10

score 0 · Accepted Answer · answered May 28 '14 at 14:57

0

Expect uses a default equality comparer to compare your objects which compares them by reference.you need to implement a custom equality comparer and use that comparer with Except method.

You can find example on MSDN if you don't know how to implement IEqualityComparer<T> for your type.

answered May 28 '14 at 14:57

Selman Genç

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how can i do it when i have two lists? in your example it compares two single objects. could you give me an example please – Eray Geveci May 28 '14 at 16:22

score 0 · Answer 2 · answered May 28 '14 at 14:57

0

You need to do like this:

var ListC = ListA.Except(ListB).Union(ListB.Except(ListA))

answered May 28 '14 at 14:57

Ehsan Sajjad

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when i add your solution, i get 5 results instead of one – Eray Geveci May 28 '14 at 15:02

score 0 · Answer 3 · answered May 28 '14 at 14:58

I would recommend you override the Equals() and GetHashCode() so that the comparison is as you'd expect.

public class Exceptions
{
   public override bool Equals(object o)
   {
      return this.Equals(o as Exceptions);
   }

   public bool Equals(Exceptions ex)
   {
       if(ex == null)
          return false;
       else
       {
           // Do comparison here
       }
   }
}

score 0 · Answer 4 · answered May 28 '14 at 15:04

0

A Linq alternative, there could be a much faster approach: HashSet.SymmetricExceptWith():

var exceptions = new HashSet(listA);

exceptions.SymmetricExceptWith(listB);

answered May 28 '14 at 15:04

dekajoo

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how to get the difference of two list<> objects ?

4 Answers4