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Sort a Linq query

Posted on 2014-09-15
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Last Modified: 2016-02-15
Experts, I am trying to figure out how to order this query Descending. Please help...
        Dim query = From company In dt.AsEnumerable
                    Select company.Field(Of String)("Company")
                    Distinct

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Question by:Basicfarmer
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6 Comments
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 500 total points
ID: 40324508
Dim query = From company In dt.AsEnumerable
            Order By company.Field(Of String)("Company") Descending
            Select company.Field(Of String)("Company")
            Distinct

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Author Closing Comment

by:Basicfarmer
ID: 40324511
Thanks, i was doing that but after the select and it wouldn't work like that.
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LVL 63

Expert Comment

by:Fernando Soto
ID: 40324527
Hi Basicfarmer;

The Distinct method call returns an unordered collection and so if you attempted to do it before the Distinct call it would not work. You need to do the ordering after the call to Distinct as shown below.

Dim query = (From company In dt.AsEnumerable
             Select company.Field(Of String)("Company")
             Distinct).OrderByDescending(Function(c) c) 

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Author Comment

by:Basicfarmer
ID: 40325801
Fernando, thanks for the comment.
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LVL 63

Expert Comment

by:Fernando Soto
ID: 40325844
Hi Basicfarmer;

Not a problem. My statement about ordering came from Microsoft documentation [here] and full statement below.

The Distinct(Of TSource)(IEnumerable(Of TSource)) method returns an unordered sequence that contains no duplicate values. It uses the default equality comparer, Default, to compare values.
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LVL 75

Expert Comment

by:käµfm³d 👽
ID: 40325995
@Fernando

That's for Distinct itself, though. If you're already dealing with an ordered collection, I doubt that Distinct is going to re-order the distinct result differently than the ordered source. I'd have to test it, though. If anything, what I am suggesting would be an implementation detail, and the most guaranteed way to ensure an ordered result would be to order after the Distinct, as you mentioned.
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