Remove duplicate values in collection

Question

I have a collection of longs List<long> myIds. I am populating the collection with id's. However I get some duplicates in the collection which I want to remove.

I have tried using distinct() on the collection but to no effect. Reordering and applying distinct() again did not help either.

What is the best way to remove these duplicates without writing custom logic?

I tried this:

mydIds.OrderBy(x => x).Distinct().ToList();

have you tried mydIds = mydIds.OrderBy(x => x).Distinct().ToList() ? — Liel
– Liel, Commented Jun 1, 2013 at 14:54
Do you have a more complete code sample? I have no problem removing duplicate long values from a collection via LINQ's Distinct call; no OrderBy necessary. — Chris Sinclair
– Chris Sinclair, Commented Jun 1, 2013 at 14:56
@Steve I think that must be it. Codingjoe, you need to re-assign the result. It does not change the existing list; it creates a new list. — Chris Sinclair
– Chris Sinclair, Commented Jun 1, 2013 at 14:56
I see that my English is not that sharp, got my post edited in lightweight, but in a more understandable format :) — codingjoe
– codingjoe, Commented Jun 1, 2013 at 18:07

cuongle · Accepted Answer · 2013-06-01 14:55:46Z

7

You need to re-assign the list again since LINQ does not change list in place:

 mydIds = mydIds.Distinct().ToList();

answered Jun 1, 2013 at 14:55

cuongle

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codingjoe Over a year ago

Ahh I feel so stupid. I actually had it working with myIds.Distict().ToList(); I had my breakpoint on a wrong collection variable. :/

Tom Fobear · Accepted Answer · 2013-06-01 15:00:09Z

3

Alternatively if you are using 3.5 and above:

var hs = new HashSet<int>(myIds);

The hashset will be populated by the list. If the list contains duplicate entries they will be ignored. No exception will be thrown.

answered Jun 1, 2013 at 15:00

Tom Fobear

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Comments

Steve · Accepted Answer · 2013-06-01 14:59:10Z

1

You don't reassing the result of the Distinct to a List object

List<long> id = new List<long>() {20,50,34, 20, 21, 45, 50, 900, 34, 20};
id = id.Distinct().ToList();
id.ForEach(x => Console.WriteLine(x));

answered Jun 1, 2013 at 14:59

Steve

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