Quick class for determining changes (additions, removals) in lists

ListDiff.cs

public static class ListDiff
{
    public static List<ListDiffItem<T>> GetDiff<T>(List<T> oldList, List<T> newList, Func<T, T, bool> equalsFunction = null)
    {
        var combined = new List<ListDiffItem<T>>();

        foreach(var i in newList)
        {
            var diff = new ListDiffItem<T>();
            diff.Item = i;

            var existing = equalsFunction != null ? oldList.Any(p => equalsFunction(p, i)) : oldList.Contains(i);
            diff.Status = existing ? "existing" : "added";

            combined.Add(diff);
        }

        foreach (var i in oldList)
        {
            var existing = equalsFunction != null ? newList.Any(p => equalsFunction(p, i)) : newList.Contains(i);

            if (!existing)
            {
                var diff = new ListDiffItem<T>();
                diff.Item = i;
                diff.Status = "removed";

                var originalPosition = oldList.IndexOf(i);
                var newPosition = combined.Count < originalPosition ? combined.Count : originalPosition;
                combined.Insert(newPosition, diff);
            }
        }

        return combined;
    }
}

ListDiffItem.cs

public class ListDiffItem<T>
{
    public T Item { get; set; }
    public string Status { get; set; }
}

Usage.cs

var combined = ListDiff.GetDiff(oldProcedures, newProcedures, (p1, p2) => p1.ProcedureID == p2.ProcedureID)