Efficiently merge string arrays in .NET, keeping distinct values

Question

I\'m using .NET 3.5. I have two string arrays, which may share one or more values:

string[] list1 = new string[] { \"apple\", \"orange\", \"banana\" };
string[]         


        

Answer 1

Why do you imagine that it would be inefficient? As far as I'm aware, both Concat and Distinct are evaluated lazily, using a HashSet behind the scenes for Distinct to keep track of the elements which have already been returned.

I'm not sure how you'd manage to make it more efficient than that in a general way :)

EDIT: Distinct actually uses Set (an internal class) instead of HashSet, but the gist is still correct. This is a really good example of just how neat LINQ is. The simplest answer is pretty much as efficient as you can achieve without more domain knowledge.

The effect is the equivalent of:

public static IEnumerable DistinctConcat(IEnumerable first, IEnumerable second)
{
    HashSet returned = new HashSet();
    foreach (T element in first)
    {
        if (returned.Add(element))
        {
            yield return element;
        }
    }
    foreach (T element in second)
    {
        if (returned.Add(element))
        {
            yield return element;
        }
    }
}