Is it effective to use HashSet to avoid duplicates?

Question

public IEnumerable<string> ListFoldersInternal(IEnumerable<CloudBlobDirectory> folders)
{
    return new HashSet<string>(folders.Select(x => x.Prefix));
}

Is it a good choice to use HashSet to avoid duplicates and return IEnumerable?

Any ideas to improve this code?

It's the most efficient way http://stackoverflow.com/questions/30366669/most-efficient-way-to-remove-duplicates-from-a-list — fubo, Jul 19 '16 at 11:40
If you call `ToArray()`, you might as well make the return type `CloudItem[]`. If the return type is `IList`, just call `ToList()` — Dennis_E, Jul 19 '16 at 11:42
They made a method for the exact purpose of avoiding duplicates. It's called `Distinct()`. — Dennis_E, Jul 19 '16 at 11:45
Your ListFolders method does not make use of your ListFoldersInternal method? if not then I'd rename them just because the implications could be confusing. — leetibbett, Jul 19 '16 at 11:49

score 4 · Answer 1 · answered Jul 19 '16 at 11:45

A more readable way might be to use the LINQ extension Distinct:

return folders.Select(x => x.Prefix).Distinct();

It is implemented in a similar fashion (using its own cut-down hash set), although it evaluates lazily (yielding after returning each unique item).

score 2 · Accepted Answer · answered Jul 19 '16 at 11:43

Using Hashset is good idea and definitely an effective way to avoid duplicates. The MSDN says:

The HashSet<T> class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.

If you want you can use LINQ as well like

List<T> myList = ......;
List<T> removeDuplicates = myList.Distinct().ToList();

Is it effective to use HashSet to avoid duplicates?

2 Answers2