C# class instance comparison, distinct

Question

4.43/5 (3 votes)

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Hello Guys,
I was wondering if anyone knows a better way to get a distinct from List<some_class> not using any helper classes.

Currently I have this (I have simplified this):

C#

class A
{
int X, Y;
public A(int xx, int yy)
{ X = xx; Y = yy;}
}

//this is a helper class I want to get rid of
class helper : IEqualityComparer<A>
{
public bool Equals(A x, A y)
{return x.X == y.X && x.Y == y.Y;}

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

List<A> class_array = new List<A>
class_array.Add(new A(1, 1));
class_array.Add(new A(1, 1));
class_array.Add(new A(2, 2));
class_array.Add(new A(2, 2));

class_array = class_array.Distinct(new helper()).ToList()

Anyone know a better solution for the situation? The reason I need this is that I have multiple class arrays to compare and I dont really want to have helper comparison classes for each... This just does not sound right...

Thank you in advance!

Posted 4-Feb-14 21:47pm

MK-Gii

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3 solutions

Solution 4

Just for variety:

C#

List<A> ADeDupe = class_array
    .Select(a => new {X = a.X, Y = a.Y})
        .Distinct()
            .ToList()
                .Select(a => new A(a.X, a.Y))
                    .ToList();

imho, your code will be more maintainable in the future if you implement the custom Comparer, and simply use 'Distinct, rather than using "tricky" Linq.

Posted 4-Feb-14 23:48pm

BillWoodruff

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Maarten Kools · Accepted Answer · 2014-02-04T21:58:00

From the documentation[^]:

The default equality comparer, Default, is used to compare values of the types that implement the IEquatable<t>[^] generic interface. To compare a custom data type, you need to implement this interface and provide your own GetHashCode and Equals methods for the type.

So class A would need to implement this interface.

-Edit-
This works fine for me:

C#

class A : IEquatable<A>
{
	int X, Y;
 
	public A(int xx, int yy) { X = xx; Y = yy; }	
	public override bool Equals(object other) { return Equals((A)other); }	 // Note that this implementation doesn't follow proper standards. Always check for null values, or objects of a different type and handle them accordingly.
	public bool Equals(A other) { return X == other.X && Y == other.Y; }	
	public override int GetHashCode() { return (X + Y).GetHashCode(); }
}

Sampath Lokuge · Accepted Answer · 2014-02-04T22:17:00

Solution 3

Try is as below.

Note:I didn't test.Please check that.

XML

List<A> distinct =
  class_array
  .GroupBy(a => new {a.X,a.Y})
  .Select(g => g.First())
  .ToList();

Posted 4-Feb-14 22:17pm

Sampath Lokuge

Comments

MK-Gii 5-Feb-14 4:39am

That worked. Thanks.

Sampath Lokuge 5-Feb-14 4:52am

Glad to hear that it helped! :)