Comparing two collections for equality irrespective of the order of items in them

Question

I would like to compare two collections (in C#), but I\'m not sure of the best way to implement this efficiently.

I\'ve read the other thread about Enumerable.Sequen

Answer 1

In the case of no repeats and no order, the following EqualityComparer can be used to allow collections as dictionary keys:

public class SetComparer : IEqualityComparer> 
where T:IComparable
{
    public bool Equals(IEnumerable first, IEnumerable second)
    {
        if (first == second)
            return true;
        if ((first == null) || (second == null))
            return false;
        return first.ToHashSet().SetEquals(second);
    }

    public int GetHashCode(IEnumerable enumerable)
    {
        int hash = 17;

        foreach (T val in enumerable.OrderBy(x => x))
            hash = hash * 23 + val.GetHashCode();

        return hash;
    }
}

Here is the ToHashSet() implementation I used. The hash code algorithm comes from Effective Java (by way of Jon Skeet).