How do I remove objects with a combination of duplicate of two properties from List with linq?

Question

Same question as this one but I need to remove objects with a combination of duplicate of two properties from List.

There is a set of objects, objects have age and Name:

21 Carl
23 Vladimir
25 Bob
21 Olivia
21 Carl
30 Jacob
23 Vladimir

Output list should contain:

21 Carl
23 Vladimir
25 Bob
21 Olivia
30 Jacob

How do I remove it?

Possible duplication https://stackoverflow.com/questions/1606679/remove-duplicates-in-the-list-using-linq — Mario Mitterbauer, Jan 05 '19 at 19:42
One possible solution, sort the list, and then any dups will be consecutive. — Flydog57, Jan 05 '19 at 20:11
This question is answered here: https://stackoverflow.com/questions/11811110/select-distinct-by-two-properties-in-a-list — M.Hazara, Jan 05 '19 at 21:18

score 1 · Accepted Answer · answered Jan 05 '19 at 19:55

Try this:

  public class KeyValueClass
    {
        public int Age { get; set; }
        public string Name { get; set; }
    }

    private void DoTheJob()
    {

        var myList = new List<KeyValueClass>
        {
            new KeyValueClass {Age = 21, Name = "Carl"},
            new KeyValueClass {Age = 23, Name = "Vladimir"},
            new KeyValueClass {Age = 25, Name = "Bob"},
            new KeyValueClass {Age = 21, Name = "Olivia"},
            new KeyValueClass {Age = 21, Name = "Carl"},
            new KeyValueClass {Age = 30, Name = "Jacob"},
            new KeyValueClass {Age = 23, Name = "Vladimir"},
        };

        var myDistinctList = myList.GroupBy(x => new { x.Age, x.Name })
            .Select(c => c.First()).ToList();
    }

score 1 · Answer 2 · answered Jan 06 '19 at 10:14

You can use Distinct() from the Linq namespace and a IEqualityComparer:

class Program
{
    static void Main(string[] args)
    {


        List<KeyValueClass> myList = new List<KeyValueClass>
            {
                new KeyValueClass {Age = 21, Name = "Carl"},
                new KeyValueClass {Age = 23, Name = "Vladimir"},
                new KeyValueClass {Age = 25, Name = "Bob"},
                new KeyValueClass {Age = 21, Name = "Olivia"},
                new KeyValueClass {Age = 21, Name = "Carl"},
                new KeyValueClass {Age = 30, Name = "Jacob"},
                new KeyValueClass {Age = 23, Name = "Vladimir"},
            };

        var myDistincList = myList.Distinct(new KeyValueEqualityComparer());

        foreach (var item in myDistincList) { Console.WriteLine("Age: {0}, Name:{1}", item.Age, item.Name); }

        Console.ReadKey();
    }
}


public class KeyValueClass 
{
    public int Age { get; set; }
    public string Name { get; set; }
}



class KeyValueEqualityComparer : IEqualityComparer<KeyValueClass>
{
    public bool Equals(KeyValueClass x, KeyValueClass y)
    {
        if (x == null || y == null) return false;
        if (x.Age == y.Age && x.Name.Equals(y.Name)) return true;
        return false;
    }

    public int GetHashCode(KeyValueClass obj)
    {
        return (obj.Age + obj.Name).GetHashCode() + 387;
    }
}

score 0 · Answer 3 · answered Jan 06 '19 at 05:38

Just use an ISet to avoid the overhead and slow performance of a List:

public class Person : IEquatable<Person> 
{
    public int Age { get; private set;}
    public string Name { get; private set;}

    public bool override Equals(Person other){
        return other.Age == Age && other.Name.Equals(Name);
    }

    public override int GetHashCode(){
        return Age.GetHashCode() ^ Name.GetHashCode();
    }
}

private IEnumerable<Person> MakeUniqueList(IEnumerable<Person> input){
    return new HashSet<Person>(input);
}

In order to actually remove, which will be quite slow performance wise (but it will save on memory usage), use List.Remove(T) https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1.remove?view=netframework-4.7.2

How do I remove objects with a combination of duplicate of two properties from List with linq?

3 Answers3