[Visual C#]兩個List相減

原本是想要做兩個List<string>相減，結果找到個好方法：

        public static IEnumerable Subtract(IEnumerable source, IEnumerable other)
        {
            return Subtract(source, other, EqualityComparer.Default);
        }

        public static IEnumerable Subtract(IEnumerable source, IEnumerable other, IEqualityComparer comp)
        {
            Dictionary dict = new Dictionary(comp);
            foreach(T item in source)
            {
                dict[item] = null;
            }

            foreach(T item in other)
            {
                dict.Remove(item);
            }

            return dict.Keys;
        }

參考資料：
http://stackoverflow.com/questions/2266682/how-to-substract-one-generic-list-from-another-in-c2-0

備註：C#預設交集操作：
http://msdn.microsoft.com/zh-tw/library/bb460136.aspx