Compare Two Arrays Of Different Lengths and Show Differences

Question

Problem:
I have two arrays that can possibly be different lengths. I need to iterate through both arrays and find similarities, additions, and deletions.

Answer 1

I went ahead and hand-coded one and use the example in the accepted answer, and the hand-coded one performs a little better. I handled outputting my strings a little differently. Other factors to consider include whether the Except make a sorted copy of the array (since it cannot assume it's sorted) or whether it makes some kind of hash or a linear search (it's actually restricted to IEnumerable - for very large arrays which are already sorted, this could be a problem). You could change mine to compare IEnumerable (which is more general) instead of IComparable[].

static void ArrayCompare(IComparable[] Old, IComparable[] New)
{
    int lpOld = 0;
    int lpNew = 0;
    int OldLength = Old.Length;
    int NewLength = New.Length;
    while (lpOld < OldLength || lpNew < NewLength)
    {
        int compare;

        if (lpOld >= OldLength) compare = 1;
        else if (lpNew >= NewLength) compare = -1;
        else compare = Old[lpOld].CompareTo(New[lpNew]);

        if (compare < 0)
        {
            Debug.WriteLine(string.Format("[Removed] {0}", Old[lpOld].ToString()));
            lpOld++;
        }
        else if (compare > 0)
        {
            Debug.WriteLine(string.Format("[Added] {0}", New[lpNew].ToString()));
            lpNew++;
        }
        else
        {
            Debug.WriteLine(string.Format("[Same] {0}", Old[lpOld].ToString()));
            lpOld++;
            lpNew++;
        }
    }
}

static void ArrayCompare2(IComparable[] Old, IComparable[] New) {
    var diff = New.Except( Old );
    var inter = New.Intersect( Old );
    var rem = Old.Except(New);

    foreach (var s in diff)
    {
        Debug.WriteLine("Added " + s);
    }

    foreach (var s in inter)
    {
        Debug.WriteLine("Same " + s);
    }

    foreach (var s in rem)
    {
        Debug.WriteLine("Removed " + s);
    }
}

static void Main(string[] args)
{
    String[] Foo_Old = {"test1", "test2", "test3"};
    String[] Foo_New = {"test1", "test2", "test4", "test5"};
    String[] Bar_Old = {"test1", "test2", "test4"};
    String[] Bar_New = {"test1", "test3"};

    Stopwatch w1 = new Stopwatch();
    w1.Start();
    for (int lp = 0; lp < 10000; lp++)
    {
        ArrayCompare(Foo_Old, Foo_New);
        ArrayCompare(Bar_Old, Bar_New);
    }
    w1.Stop();

    Stopwatch w2 = new Stopwatch();
    w2.Start();
    for (int lp = 0; lp < 10000; lp++)
    {
        ArrayCompare2(Foo_Old, Foo_New);
        ArrayCompare2(Bar_Old, Bar_New);
    }
    w2.Stop();

    Debug.WriteLine(w1.Elapsed.ToString());
    Debug.WriteLine(w2.Elapsed.ToString());
}