distinct with LINQ

Question

 var sourceId =
            (from workstation in db.station
             join letter in db.letter on workstation.id equals letter.Site_Id
             where ThatDate < DateTime.Now.AddYears(-1)
             select workstatio).ToList();

This produces a list which will print out repeats if more than one, how can I use .distinct?

Please advise, thanks

possible duplicate of [LINQ distinct on class item?](http://stackoverflow.com/questions/1930654/linq-distinct-on-class-item) — Jon Egerton, Jan 11 '13 at 15:37

Sean Barlow · Accepted Answer · 2013-01-11T16:15:10.903

0

 var sourceId =
            (from workstation in db.station
             join letter in db.letter on workstation.id equals letter.Site_Id
             where ThatDate < DateTime.Now.AddYears(-1)
             select workstation).Distinct().ToList();

Take a look at this

http://msdn.microsoft.com/en-us/library/bb338049.aspx

edited Jan 11 '13 at 16:15

answered Jan 11 '13 at 15:37

Sean Barlow

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6
11

that won't work as it will compare the object pointers and decide that they're all different objects – David Jan 11 '13 at 15:39
Then you will need to do something like this http://msdn.microsoft.com/en-us/library/bb338049.aspx – Sean Barlow Jan 11 '13 at 16:14

TKharaishvili · Answer 2 · 2013-01-14T15:56:42.520

You might want to have a look at DistinctBy method in MoreLinq. Where you can pass a lambda expression as a parameter.

In your example it would look something similar to this:

var sourceId =
        (from workstation in db.station
         join letter in db.letter on workstation.id equals letter.Site_Id
         where ThatDate < DateTime.Now.AddYears(-1)
         select workstatio).DistinctBy(ws => ws.Id).ToList();

You can also use DistinctBy with multiple properties:

var sourceId =
        (from workstation in db.station
         join letter in db.letter on workstation.id equals letter.Site_Id
         where ThatDate < DateTime.Now.AddYears(-1)
         select workstatio).DistinctBy(ws => new {Id = ws.Id, OtherProperty = ws.OtherProperty}).ToList();

Btw, instead of reference-comparing, the equality of anonymous type instances is determined by comparing each one of their properties.

I have recently found an interesting discussion around this topic where Anders Hejlsberg himself suggests the solution to this problem. You can read it here.

distinct with LINQ

2 Answers2