How could distinct multi array list on c#

Question

Consider objModels is object of ChildModel class

public class ChildModel
{
public string Title { get; set; }
public long Id { get; set; }
}

It has some data like: title,id: a,1 b,1 a,1

Two of these data are same, and after distinct it could be like: a,1 b,1

Question is how could I distinct it on c#

List<ChildModel> obj= objModels.ToList();

Also these aren't help

objModels.Distinct();
obj.Distinct();

you have to override Equals and GetHashCode, like this so, msdn — Lei Yang
– Lei Yang, Commented May 12, 2017 at 10:24
@ShahroozAnsari thank you man, but "DistinctBy" isn't exist when I try to use — asa
– asa, Commented May 12, 2017 at 10:34
look at this link msdn.microsoft.com/en-us/library/bb338049.aspx — Shahrooz Ansari
– Shahrooz Ansari, Commented May 12, 2017 at 10:39

sachin · Accepted Answer · 2017-05-12 10:26:44Z

1

You could use a library named MoreLINQ

This is the query you could use with MoreLINQ to find elements that are distinct by multiple properties:

var query = objModels.DistinctBy(p => new { p.Id, p.Title});

answered May 12, 2017 at 10:26

sachin

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Comments

Shahrooz Ansari · Accepted Answer · 2017-05-12 10:40:16Z

0

try this:

var answer= obj.DistinctBy(p => new { p.Id , p.Title });

and check this link for other way

edited May 12, 2017 at 10:40

answered May 12, 2017 at 10:27

Shahrooz Ansari

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1 Comment

Matt Hogan-Jones Over a year ago

DistinctBy requires the MoreLINQ library.

Mobaruk H · Accepted Answer · 2017-05-12 10:53:54Z

I would do the following:

            namespace ConsoleApplication7
            {
                class Program
                {
                    static void Main()
                    {
                        List<ChildModel> list = new List<ChildModel>();
                        list.Add(new ChildModel { Title = "a", Id = 1 });
                        list.Add(new ChildModel { Title = "b", Id = 1 });
                        list.Add(new ChildModel { Title = "a", Id = 1 });

                        var x = list.Distinct(new ChildModelComparer()).ToList();

                        var y = x; //This has only got two child items.

                    }
                }
                class ChildModelComparer : IEqualityComparer<ChildModel>
                {
                    public bool Equals(ChildModel x, ChildModel y)
                    {
                        return x.Id.Equals(y.Id) && x.Title.Equals(y.Title);
                    }

                    public int GetHashCode(ChildModel obj)
                    {
                        if (string.IsNullOrEmpty(obj.Title) && obj.Id == 0)
                        {
                            return 0;
                        }
                        return $"{obj.Id}{obj.Title}".GetHashCode();
                    }
                }
                public class ChildModel
                {
                    public string Title { get; set; }
                    public long Id { get; set; }
                }
            }

I have used IEqualityComparer so that I can use the second overload of distinct.

WhileTrueSleep · Accepted Answer · 2017-05-12 11:41:05Z

0

you can use .GroupBy:

var result= obj
  .GroupBy(p => p.Title)
  .Select(g => g.First()) // choose which one
  .ToList();

edit: if you want to GroupBy more than one Property you can just change p.Title to new {p.Title, p.Id} like so

var result= obj
  .GroupBy(p => new {p.Title, p.Id})
  .Select(g => g.First()) // choose which one
  .ToList();

edited May 12, 2017 at 11:41

answered May 12, 2017 at 10:24

WhileTrueSleep

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7 Comments

Shahrooz Ansari Over a year ago

this is so baad way to dothis

sachin Over a year ago

This would only Group items by Title, he needs items to be distinct by both Id and Title.

asa Over a year ago

Guys this works on this code, I checking, but on c# I haven't "DistinctBy" during a list like this

WhileTrueSleep Over a year ago

@sachin edited my post - was not really clear for me if OP wants more or less properties to be grouped

WhileTrueSleep Over a year ago

@Shahrooz Ansari why is this a bad way?

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