Distinct in linq?

Question

I am wondering how can I achieve this?

I want to get only distinct names from a collection of objects

MyObject a = new Object(); a.Name = 'One'; a.Value = '10'; MyObject b = new Object(); b.Name = 'One'; b.Value = '15'; MyObject c = new Object(); c.Name = 'Two'; c.Value = '10';

So I want to get only back the name. I don't care about the value in this case just the name.

So I tried

//add all the objects to a collection.

myCollection.Disinct()..Select(x => new MyClassToStore() {Text = x.Name, Value = x.Name}).ToList());

However I need to do distinct at the property level not at the object level. So I want back "One" and "Two". Right now I get "One", "One" and "Two" back.

I see a library called morelinq but I not sure if I should use it as it still in beta and does not seem to be developed on anymore.

Plus a whole library for one extract query I am not sure if it is worth it.

Related: stackoverflow.com/questions/489258/…

Cameron
– Cameron

2011-04-09 21:57:21 +00:00
Commented Apr 9, 2011 at 21:57 — Cameron
– Cameron, Commented Apr 9, 2011 at 21:57

Marino Šimić · Accepted Answer · 2011-04-09 21:50:57Z

24

Maybe something like this can help?

var distinctItems = items .GroupBy(x => x.PropertyToCompare) .Select(x => x.First());

answered Apr 9, 2011 at 21:50

Marino Šimić

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2 Comments

chobo2 Over a year ago

how could I get stick it into MyClassToStore

Marino Šimić Over a year ago

var distinctitems = myCollection.GroupBy(x => x.Name).Select(x => x.First()).Select(new MyClassToStore() {Text = x.Name, Value = x.Name}) i suppose, altough i did not get exactly what you need. because using the same property (name) twice is a bit awkward... I think that you should listen to Cameron if you need just names...

PHeiberg · Accepted Answer · 2011-04-09 22:01:03Z

This populates both the Text and Value fields:

 myCollection.Select(x => x.Name).Distinct() .Select(x => new MyClassToStore { Text = x, Value = x }).ToList();

Cameron · Accepted Answer · 2011-04-09 21:52:19Z

If you just want back distinct names, you can use:

myCollection.Select(x => x.Name).Distinct().ToList();

Alessandro Incarnati · Accepted Answer · 2014-08-08 18:53:41Z

You can implement your class so the linq distinct operator does not use the default equality comparer.

class YourClass:IEquatable<YourClass> {

... Your implementation details. ...

 public bool Equals(YourClass other) { if (Object.Equals(this, other)) { return true; } else { if(Name == other.Name && Value == other.Value) { return true; } else { return false; } } } public override int GetHashCode() { return Name.GetHashCode() ^ Value.GetHashCode(); } }

Chuck Savage · Accepted Answer · 2011-04-10 01:06:35Z

Personally I suggest you override operator == and != and determine how and why an object is unique there. Then use the Distinct() call on the collection.

You do have to be careful with null values, see Microsoft's Guidelines for Overloading Equals() and Operator == (C# Programming Guide).

To be clear, do not override the == or != operator in any sort of global context. What's suggested here is to override the Equals and == operator your class inherits from object

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