linq去重方法

        /// 


        /// 用于Linq的去重,扩展方法需要放到静态类中
        /// 
        /// 
        /// 
        /// 
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        /// 
        public static IEnumerable DistinctBy(this IEnumerable source, Func keySelector)
        {
            HashSet seenKeys = new HashSet();
            foreach (TSource element in source)
            {
                if (seenKeys.Add(keySelector(element)))
                {
                    yield return element;
                }
            }
        }


调用方法：
 list.DistinctBy(tmp => new { tmp.CountryName, tmp.VisaTypeName });