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](http://stackoverflow.com/questions/9317582/correct-way-to-override-equals-and-gethashcode), [msdn](https://msdn.microsoft.com/en-us/library/ms182358.aspx) — Lei Yang, May 12 '17 at 10:24
@ShahroozAnsari thank you man, but "DistinctBy" isn't exist when I try to use — asa, May 12 '17 at 10:34
look at this link https://msdn.microsoft.com/en-us/library/bb338049.aspx — Shahrooz Ansari, May 12 '17 at 10:39

score 1 · Answer 1 · answered May 12 '17 at 10:26

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 '17 at 10:26

sachin

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WhileTrueSleep · Answer 2 · 2017-05-12T11:41:05.507

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 '17 at 11:41

answered May 12 '17 at 10:24

WhileTrueSleep

1,524
1
19
32

this is so baad way to dothis – Shahrooz Ansari May 12 '17 at 10:29
This would only Group items by Title, he needs items to be distinct by both Id and Title. – sachin May 12 '17 at 10:29
1

Guys this works on this code, I checking, but on c# I haven't "DistinctBy" during a list like this – asa May 12 '17 at 10:33
@sachin edited my post - was not really clear for me if OP wants more or less properties to be grouped – WhileTrueSleep May 12 '17 at 11:44
@Shahrooz Ansari why is this a bad way? – WhileTrueSleep May 12 '17 at 13:27
@WhileTrueSleep watch this links http://stackoverflow.com/questions/22066346/linq-groupby-vs-distinct http://stackoverflow.com/questions/24869683/group-by-clause-vs-distinct – Shahrooz Ansari May 12 '17 at 15:41
@ShahroozAnsari maybe it is faster .. maybe its not! No measurements of performance there. Seems more like a personal preference to take distinct over groupby (both fullfill the req. of OP). – WhileTrueSleep May 15 '17 at 06:21

Shahrooz Ansari · Accepted Answer · 2017-05-12T10:40:16.037

0

try this:

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

and check this link for other way

edited May 12 '17 at 10:40

answered May 12 '17 at 10:27

Shahrooz Ansari

2,637
1
13
21

`DistinctBy` requires the MoreLINQ library. – Matt Hogan-Jones May 12 '17 at 10:29

score 0 · Answer 4 · answered May 12 '17 at 10:53

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. — Mobaruk H, May 12 '17 at 10:55

How could distinct multi array list on c#

4 Answers4