C# group by a list contains another class [duplicate]

Question

I have two classes as below:

public class result
{
    public person identity { get; set; }
}

public class person
{
    public string name { get; set; }

    public string family { get; set; }
}

I have List<result> which has some repetitive data. I want to get rid of repetitive data by System.Linq.GroupBy

I searched a lot and I think the best answer I've found was here, so I have simulated my code as below:

class Program
{
    static void Main(string[] args)
    {
        person p1 = new person();
        p1.name = "Bill"; p1.family = "Gates";
        person p2 = new person();
        p2.name = "Satoshi"; p2.family = "Nakamoto";
        person p3 = new person();
        p3.name = "AmirAli"; p3.family = "Sam";

        List<result> lst = new List<result>();
        List<List<result>> lstGrp = new List<List<result>>();

        lst.Add(new result { identity = p1 });
        lst.Add(new result { identity = p1 });
        lst.Add(new result { identity = p1 });
        lst.Add(new result { identity = p2 });
        lst.Add(new result { identity = p2 });
        lst.Add(new result { identity = p2 });
        lst.Add(new result { identity = p3 });
        lst.Add(new result { identity = p3 });
        lst.Add(new result { identity = p3 });

        lstGrp = lst
            .GroupBy(r => r.identity)
            .Select(grp => grp.ToList())
            .ToList();

        foreach (List<result> list in lstGrp)
        {
            foreach (result item in list)
            {
                Console.WriteLine(item.identity.name + " " + item.identity.family);
            }
        }
    }
}

As shown, I have repetitive person in different result but I want to see each person once in my Console as:

But what I faced at last was:

How should I change my code to get the result I want?

Thanks a lot in advance.

person p1 = new person(); p1.name = "Bill"; p1.family = "Gates"; person p2 = new person(); p1.name = "Satoshi"; p1.family = "Nakamoto"; person p3 = new person(); p1.name = "AmirAli"; p1.family = "Sam"; is here a typo? you only set name and family to p1 Person — demo
– demo, Commented Jun 3, 2021 at 7:17
@demo Really sorry! Disadvantage of copy pasting! But I still has the issue, I did it in another project and still not work so I simulated my project as shown. thanks. — Amirali Samiei
– Amirali Samiei, Commented Jun 3, 2021 at 7:25
The only real issue in your code is that you are iterating each list within the collection of groups, when you could just be iterating the collection of groups and displaying the key. See duplicate for the correct way to approach this. That said, I'll note that the next problem you're probably going to run into is that while the above works fine for grouping, it's only because you're using the same instance for each result that uses the same person. ... — Peter Duniho
– Peter Duniho, Commented Jun 3, 2021 at 7:28
... It's likely that in a real-world situation, you'll have multiple person instances that use the same values and will want to implement IEquatable<person> for grouping to work like you expect it to. — Peter Duniho
– Peter Duniho, Commented Jun 3, 2021 at 7:28

demo · Accepted Answer · 2021-06-03 07:23:45Z

2

I think that what you are really looking for is "distinct" and not "groupBy". See here Select distinct using linq .

https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.distinct?view=net-5.0

What they say about distinct:

Returns distinct elements from a sequence.

Example:

person p1 = new person();
p1.name = "Bill";
p1.family = "Gates";

person p2 = new person();
p2.name = "Satoshi";
p2.family = "Nakamoto";

person p3 = new person();
p3.name = "AmirAli";
p3.family = "Sam";

List<result> lst = new List<result>();
List<person> lstGrp = new List<person>();
lst.Add(new result{identity = p1});
lst.Add(new result{identity = p1});
lst.Add(new result{identity = p1});
lst.Add(new result{identity = p2});
lst.Add(new result{identity = p2});
lst.Add(new result{identity = p2});
lst.Add(new result{identity = p3});
lst.Add(new result{identity = p3});
lst.Add(new result{identity = p3});

lstGrp = lst.Select(r => r.identity).Distinct().ToList();
foreach (var item in lstGrp)
{
    Console.WriteLine(item.name + " " + item.family);
}

edited Jun 3, 2021 at 7:23

demo

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answered Jun 3, 2021 at 7:18

Alex Spitz

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1 Comment

demo Over a year ago

@AkshayGaonkar do you think List<List<result>> is better?

user2471755 · Accepted Answer · 2021-06-03 07:21:07Z

1

You assigned all Name and Family to the same variable p1

answered Jun 3, 2021 at 7:21

user2471755

233 bronze badges

1 Comment

Amirali Samiei Over a year ago

Really sorry! Disadvantage of copy pasting! But I still has the issue, I did it in another project and still not work so I simulated my project as shown. thanks

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