/// <summary>
        /// Method to join together selected categories in the listview.
        /// </summary>
        /// <param name="categoriesIndices">Indices of selected categories.</param>
        public void JoinCategories(ArrayList categoriesIndices)
        {
            categoriesIndices.Sort();
            CategoryType firstType = new CategoryType();
            String newName;
            newName = "Join < ";
            if (categoriesIndices.Count > 0)
            {
                firstType = this.GetCategory(Convert.ToInt32(categoriesIndices[0])).CatType;
            }
            else
            {
                return;
            }
            Category newMultiSet = new Category();
            newMultiSet.CatType = firstType;
            bool firstRun = true;
            foreach (int index1 in categoriesIndices)
            {
                //cannot join multisets of different types
                if (this.GetCategory(index1).CatType != firstType)
                {
                    return;
                }

                //if the category is of interval type, add all of the intervals to the new category
                if (newMultiSet.CatType == CategoryType.Interval)
                {
                    foreach (Interval tempInterval in this.GetCategory(index1).GetIntervals())
                    {
                        newMultiSet.AddInterval(tempInterval);
                    }
                }

                //add all of the enum values otherwise
                else
                {
                    newMultiSet.AddSingleSet(this.GetCategory(index1).Set);
                }
                if (firstRun)
                {
                    newName = newName + this.GetCategory(index1).Name;
                    firstRun = false;
                }
                else
                {
                    newName = newName + "; " + this.GetCategory(index1).Name;
                }
            }
            newName = newName + " >";
            newMultiSet.Name = newName;
            int offset = 0;
            foreach (object index1 in categoriesIndices)
            {
                int index = Convert.ToInt32(index1.ToString());
                this.RemoveCategory(index - offset);
                offset++;
            }
            this.AddNewCategoryDirect(newMultiSet);
            this.OnDataStructureChange();
        }