lambda 根据条件去重

    /// <summary>
    /// 去重
    /// </summary>
    public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
    {
        var seenKeys = new HashSet<TKey>();
        return source.Where(element => seenKeys.Add(keySelector(element)));
    }