How to remove duplicates from a StringCollection in c#? I was looking for a more efficient approach. StringCollection is returned from an API.
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4A more efficient approach than what?Dan Puzey– Dan Puzey2010-04-15 12:32:34 +00:00Commented Apr 15, 2010 at 12:32
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Actually what I had in mind was to traverse every entity and remove all instances except one. But now I have found one statement solution.Tasawer Khan– Tasawer Khan2010-04-16 04:41:33 +00:00Commented Apr 16, 2010 at 4:41
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4 Answers
Just use a HashSet<string> as your collection, rather than StringCollection. It is designed to prevent the addition of duplicate elements by comparing hash codes of those elements (thus being very efficient).
Edit: Since it would seem you're returned a StringCollection in the first place, then the solution should just be to loop over all the items in the StringCollection and add them to a HashSet<string>, thereby eliminating duplicates. The Enumerable.Distinct extension method would also do the job, but less efficiently I suspect, since it does use hashing (rather just normal equality testing). Something like this:
var noDuplicatesItems = stringCollection.Cast<string>().Distinct().ToArray();
13 Comments
Rowland Shaw
The OP did say the StringCollection was coming from an API.
Noldorin
@Rowland: Thanks, but really worth the down-vote? My answer still largely applies.
Claudio Redi
Good solution but... he could use it only with the framework 3.5 or above.
Noldorin
@Claudio: Yes, true... however with .NET 4.0 out now, it is likely most people are at least using .NET 3.5 for new programs. It wouldn't be too hard to implement your own
HashSet<T> also.Rowland Shaw
@Noldorin
StringCollection doesn't appear to support IEnumerable<string>, so Enumerable.Distinct() wouldn't be available? |
StringCollection s = new StringCollection();
s.Add("s");
s.Add("s");
s.Add("t");
var uniques = s.Cast<IEnumerable>();
var unique = uniques.Distinct();
foreach (var x in unique)
{
Console.WriteLine(x);
}
Console.WriteLine("Done");
Console.Read();
Not tested for efficiency.
If you're in v3.5 of the Framework (or later), then you can first convert to an IEnumerable<string>, and then call the Distinct() method on that; ie:
// where foo is your .Collections.Specialized.StringCollection
IEnumerable<string> distinctList = foo.OfType<string>.Distinct()
Comments
using linq: myCollection.Cast<string>.Distinct().ToList();
or you can use a HashSet as Noldorin proposed
1 Comment
Noldorin
No, because it's not generic. A simple
Cast<string> will convert it into a generic IEnumerable<string> however, then you can use whatever you wish.