Question

How to remove duplicates from a StringCollection in c#? I was looking for a more efficient approach. StringCollection is returned from an API.

Answer 1

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();