How to get a distinct list from a List of objects?

Question

I have a List someList.

class MyClass
{
    public int Prop1...
    public int Prop2...
    public int Prop3...
}

Answer 1

Just use the build-in function DistinctBy of Microsoft Ajax Ultility library like the sample blow:

First including library

using Microsoft.Ajax.Utilities;

then

var distinctList = yourList.DistinctBy(x => x.Prop2).ToList();

Answer 2

If you would like to Distinct your list by multiple fields, You have to create an instance of IEqualityComparer interface:

public class MyComparer : IEqualityComparer<MyModel>
{
    public bool Equals(MyModel x, MyModel y)
    {
       // compare multiple fields
        return
            x.Field1 == y.Field1 &&
            x.Field2 == y.Field2 &&
            x.Field3 == y.Field3 ;
    }

    public int GetHashCode(MyModel obj)
    {
        return 
            obj.Field1.GetHashCode() + 
            obj.Field2.GetHashCode() + 
            obj.Field3.GetHashCode();
    }
}

Then use the comparer to distinct your list:

var distinctedList = myList.Distinct(new MyComparer()).ToList();

Answer 3

Override Equals(object obj) and GetHashCode() methods:

class MyClass
{
    public int Prop1 { get; set; }
    public int Prop2 { get; set; }
    public int Prop3 { get; set; }

    public override bool Equals(object obj)
    {
        return ((MyClass)obj).Prop2 == Prop2;
    }
    public override int GetHashCode()
    {
        return Prop2.GetHashCode();
    }
}

and then just call:

List<MyClass> distinctList = someList.Distinct().ToList();

Answer 4

Since the introduction of value tuples, if you want a LINQ equivalent to SQL's DISTINCT

items.GroupBy(item => (item.prop1, item.prop2, ...)).Select(group => group.First())