LINQ 2 OBJECTS - how to select distinct ones?

Question

I have a collection of objects which are: someDate someString

I need to select objects that are different by this two fields. And I can not select it as objects in collections - I need to create new ones.

Say:

01/01/2011 "One"

01/01/2011 "Two"

(I need to note - this four are different to each other)

And I need to get:

01/01/2011 "One"

01/01/2011 "Two"

How can I achieve it?

Thanks.

Your question is unclear, particularly: "And I can not select it as objects in collections - I need to create new ones." — Jon Skeet
– Jon Skeet, Commented Jul 27, 2011 at 11:09

Jon Skeet · Accepted Answer · 2011-07-27 11:08:23Z

5

Your question is fairly unclear, but it sounds like you either just need to use Distinct after a projection:

var distinctDatesAndNames = items.Select(x => new { x.Date, x.Name })
                                 .Distinct();

or you need to use something like DistinctBy from MoreLINQ:

var distinctItems = items.DistinctBy(x => new { x.Date, x.Name });

It would really help if you could clarify your question though.

answered Jul 27, 2011 at 11:08

Jon Skeet

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2 Comments

Monochromie Over a year ago

After projection? My main problem is that I thought that "new" keyword will create an instance of anonymous object for EVERY object in incoming collection. How can Distinct() determine - which are different and which are not?

Jon Skeet Over a year ago

@Monochromie: Yes, it will create a new instance for each object - but then Distinct will use Equals and GetHashCode to find equal ones.

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