CODEWITHSUNDEEP
c#linq
mo alaz
mo alaz

Reputation: 4769

Linq Except considering only one property

I have two lists of object.

List<object1> obj1 = new List<object1>();

List<object2> obj2 = new List<object2>();

I want to do this:

obj2 = obj2.Except(obj1).ToList();

However, by reading other questions similar to mine, I understand that this doesn't work unless I override Equals.

I do not want to do that, but both obj2 and obj1 have a string property that is sufficient to see whether they are equal. If obj2.StringProperty is equivalent to obj1.StringProperty then the two can be considered equal.

Is there any way I can use Except, but by using only the string property to compare?

Upvotes: 31

Views: 30938

Answers (2)

Astrid E.
Astrid E.

Reputation: 2872

In .Net 6 you can use .ExceptBy() from System.Linq.

If your classes contain the following properties:

public class Object1
{
    public string String { get; set; }
}

public class Object2
{
    public string String { get; set; }
}

.ExceptBy() can be used like this to compare the two string properties:

var objects1 = new List<Object1>();
var objects2 = new List<Object2>();

// Populate lists

objects2 = objects2
    .ExceptBy(
        objects1.Select(obj1 => obj1.String)
        obj2 => obj2.String) // selecting the String property of Object2 for comparison
    .ToList();

Example fiddle here.

(Using .ExceptBy() has also been suggested by @mjwills in their comment, via MoreLinq.)

Upvotes: 19

JaredPar
JaredPar

Reputation: 755457

The Except method requires that the two collection types involved have the same element type. In this case the element types are different (object1 and object2) hence Except isn't really an option. A better method to use here is Where

obj2 = obj2
  .Where(x => !obj1.Any(y => y.StringProperty == x.StringProperty))
  .ToList();

Upvotes: 65

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