Generic list comparison / duplicate removal

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C#

Hello guys,
I am trying to compare 2 list of custom objects.
Here is my setup:

C#

Class <Entity>
{
     string ID;
     int Amount;

     public Entity(string _ID, int _Amount)
     {
        ID = _ID; Amount = _Amount;
     }
}

In the further code I have this:

C#

List<Entity> E1 = mew List<Entity>();
List<Entity> E2 = mew List<Entity>();

C#

E1.Add(new Entity("A1", 1));
E1.Add(new Entity("A1", 1));
E1.Add(new Entity("B1", 3));
E1.Add(new Entity("C1", 5));

E2.Add(new Entity("A1", 1));
E2.Add(new Entity("D1", 7));
E2.Add(new Entity("F1", 8));
E2.Add(new Entity("F1", 8));

So - 1st question - how to remove duplicates from these 2 lists? E1 has doubled ["A1", 1] combination and E2 has ["F1", 8] combination.

I have tried using this:

C#

E1 = E1.distinct().ToList()
E2 = E2.distinct().ToList()

But that did not help... any help would be appreciated.

Question #2.
I want to return 3rd list which would contain the items that are in list E1, but not in list #2.
I have tried this LINQ query:

C#

var distinction = (from item in E2
                  where !E1.Contains(item)
                  select item).ToList();

Though that does not quiet work - it returns items that are present in both... so I'm quiet lost in here.... I was thinking about implementing IComparable interface on Entity class, but not really sure... would appreciate if you could at least show me the right path or give some example to turn my brains on :)

Thanks in advance!

Posted 17-Jan-14 3:35am

MK-Gii

Updated 17-Jan-14 3:41am

v3

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Comments

Karthik_Mahalingam 17-Jan-14 9:59am

Solution 1 Deleted Pls ignore...
Check Solution 2

3 solutions

Solution 3

If you just don't feel like implementing an IEqualityComparer, as Karthik neatly shows you how to do, there is an alternative: you do need to override Equals in your Entity Class:

C#

public class Entity
{
     public string ID;
     public int Amount;

     public Entity(string _ID, int _Amount)
     {
        ID = _ID; Amount = _Amount;
     }

     public override bool Equals(object obj)
     {
         Entity e2 = obj as Entity;

         // edge cases ? not really necessary ?
         //if (ReferenceEquals(this, e2)) return true;

         //if (e2 == null && this != null) return false;

         //if (this == null && e2 != null) return false;

         return this.ID == e2.ID && this.Amount == e2.Amount;
     }
}

Then you can do this:

C#

List<Entity> E1 = new List<Entity>();
List<Entity> E2 = new List<Entity>();

private void TestListFilteringAndMerging(object sender, EventArgs e)
{
    E1.Add(new Entity("A1", 1));
    E1.Add(new Entity("A1", 1));
    E1.Add(new Entity("B1", 3));
    E1.Add(new Entity("C1", 5));

    E2.Add(new Entity("A1", 1));
    E2.Add(new Entity("D1", 7));
    E2.Add(new Entity("F1", 8));
    E2.Add(new Entity("F1", 8));

    // test Equals override
    // Console.WriteLine(E1[0].Equals(E2[0])).ToString());

    // eliminate duplicates in each List
    E1 = E1.GroupBy(e1 => e1.ID).Select(e2 => e2.First()).ToList();
    E2 = E2.GroupBy(e1 => e1.ID).Select(e2 => e2.First()).ToList();

    // merge two Lists and eliminate duplicates in merged List
    List<Entity> JoinE1E2 = E1.Concat(E2).GroupBy(e1 => e1.ID).Select(e2 => e2.First()).ToList();

    // examine merged List
    foreach(Entity theEntity in JoinE1E2)
    {
        Console.WriteLine(theEntity.ID + " : " + theEntity.Amount.ToString());
    }
}

However, I'd recommend you go ahead and use the solution Karthik showed you, because: I think it is more readable, probably more maintainable over time ... just all-around more "standard."

I shudder to think of trying to explain the clever use of Linq here ... even to myself :)

And, note that VS 2013 will give you a warning (but not stop compilation) that you have not over-ridden 'GetHashCode.

Posted 17-Jan-14 5:36am

BillWoodruff

Updated 17-Jan-14 7:01am

v3

Comments

Maciej Los 17-Jan-14 11:44am

+5

Karthik_Mahalingam 17-Jan-14 12:25pm

5!

Solution 4

See my past answer: how to compare dates in one array[^].

Posted 17-Jan-14 5:59am

Maciej Los

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Karthik_Mahalingam · Accepted Answer · 2014-01-17T03:55:00

Try this..

C#

using System.Collections.Generic;
using System;
using System.Linq;


class Program
{

    static void Main(string[] args)
    {
        List<entity> E1 = new List<entity>();
        List<entity> E2 = new List<entity>();
        E1.Add(new Entity("A1", 1));
        E1.Add(new Entity("A1", 1));
        E1.Add(new Entity("B1", 3));
        E1.Add(new Entity("C1", 5));

        E2.Add(new Entity("A1", 1));
        E2.Add(new Entity("D1", 7));
        E2.Add(new Entity("F1", 8));
        E2.Add(new Entity("F1", 8));
        // remove duplicates

        E1 = E1.Distinct(new EntityComparer()).ToList();
        E2 = E2.Distinct(new EntityComparer()).ToList();

        // question 2 

      var newresult = E1.Where(k => !E2.Contains(k, new EntityComparer())).ToList();   


        Console.ReadLine();
    }
}

class EntityComparer : IEqualityComparer<entity>
{ 
    public bool Equals(Entity x, Entity y)
    {
        return x.ID == y.ID; 
    }


    public int GetHashCode(Entity obj)
    {
        return 0;
    }
}

class Entity
{
    public string ID { get; set; }
    public int Amount { get; set; }

    public Entity(string _ID, int _Amount)
    {
        ID = _ID; Amount = _Amount;
    }
}