Distinct根据指定字段去重扩展方法

/// <summary>
        /// 根据指定字段去重
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TKey"></typeparam>
        /// <param name="source"></param>
        /// <param name="keySelector"></param>
        /// <returns></returns>
        public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            var seenKeys = new HashSet<TKey>();
            foreach (TSource element in source)
            {
                if (seenKeys.Add(keySelector(element)))
                {
                    yield return element;
                }
            }
        }