How to create a generic method in C# that's all applicable to many types - ints, strings, doubles etc.

Question

Let's I have a method to remove duplicates in an integer Array

 public int[] RemoveDuplicates(int[] elems)
    {
        HashSet<int> uniques = new HashSet<int>();
        foreach (int item in elems)
            uniques.Add(item);
        elems = new int[uniques.Count];
        int cnt = 0;
        foreach (var item in uniques)
            elems[cnt++] = item;
        return elems;
    }

How can I make this generic such that now it accepts a string array and remove duplicates in it? How about a double array? I know I am probably mixing things here in between primitive and value types. For your reference the following code won't compile

 public List<T> RemoveDuplicates(List<T> elems)
        {
            HashSet<T> uniques = new HashSet<T>();
            foreach (var item in elems)
                uniques.Add(item);
            elems = new List<T>();
            int cnt = 0;
            foreach (var item in uniques)
                elems[cnt++] = item;
            return elems;
        }

The reason is that all generic types should be closed at run time. Thanks for you comments

Answer 1

    public List<T> RemoveDuplicates<T>(List<T> elems)
    {                           //  ^
        HashSet<T> uniques = new HashSet<T>();
        foreach (var item in elems)
            uniques.Add(item);
        elems = new List<T>();
        int cnt = 0;
        foreach (var item in uniques)
            elems[cnt++] = item;
        return elems;
    }

Then you call it:

.RemoveDuplicates<string>(new List<string>{ "hello", "hello", "world" });

However, I suggest you use this code:

public IList<T> RemoveDuplicates<T>(IEnumerable<T> elems)
{                            //  ^
    IList<T> uniques = new List<T>();
    foreach(T item in elems)
       if(!uniques.Contains(item))
          uniques.Add(item);

    return uniques;
}

This way

1. Your function can take any IEnumerable (this include IList, or anything we can enumerate through)
2. Your function is simpler, it may not be efficient for large data-sets though, however that is subject to your average data-size. If you desire efficiency over large data-sets you can simply take the IEnumerable<> component and go from there.
3. It returns an IList<>, which is more generic to work with.

Or if you have access to .NET 3.0 / 3.5 / 4.0, use linq like the other answers suggested. Hopefully this helped illustrate Generic Methods.

Answer 2

If what you want to return a collection with duplicates removed, the functionality is built-in:

elems = elems.Distinct()

If the question is more generally about creating a generic function that works with strings, ints, doubles, etc., declare it

public IEnumerable<T> RemoveDuplicates(IEnumerable<T> elems) where T : IComparable<T>

Answer 3

Easier than writing your own function: .Distinct().ToList().