C#通用方法扩张

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1,对集合Distinct方法

    public static IEnumerable<TSource> Distinct<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector)    {        HashSet<TKey> keys = new HashSet<TKey>();        foreach (var i in source)        {            if (keys.Add(selector(i))**重点内容**)            {                yield return i;            }        }    }

2,扩展方法将任意集合转成DataSet

    /// <summary>    /// 转换成DataSet，若被转换对象为Null，则返回Null。    /// </summary>    /// <param name="obj">一个对象实例</param>    /// <returns>返回DataSet，若被转换对象为Null，则返回Null。</returns>    public static DataSet ToDataSet(this object obj)    {        if (obj == null)            return null;        if (obj is DataSet)        {            return obj as DataSet;        }        DataSet ds = new DataSet();        if (obj is DataTable)        {            ds.Tables.Add(obj as DataTable);            return ds;        }        DataTable dt = new DataTable();        ds.Tables.Add(dt);        IEnumerable<object> list = obj as IEnumerable<object>;        if (list == null)        {            var properties = obj.GetType().GetProperties().ToList();            if (properties.Count == 0)                return null;            properties.ForEach(s => dt.Columns.Add(s.Name, Nullable.GetUnderlyingType(s.PropertyType) ?? s.PropertyType));            var row = dt.NewRow();            properties.ForEach(s => row[s.Name] = s.GetValue(obj, null) ?? DBNull.Value);            dt.Rows.Add(row);        }        else        {            try            {                var properties = list.ToList()[0].GetType().GetProperties().ToList();                properties.ForEach(s => dt.Columns.Add(s.Name, Nullable.GetUnderlyingType(s.PropertyType) ?? s.PropertyType));                foreach (var i in list)                {                    var row = dt.NewRow();                    properties.ForEach(s => row[s.Name] = s.GetValue(i, null) ?? DBNull.Value);                    dt.Rows.Add(row);                }            }            catch (Exception)            {                return null;            }        }        return ds;    }

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