c＃linq查询具有其他列值的聚合数据

Question

this is my environment.

I have a datatable with this kind of structure

IDstring | Attrib1 | Attrib2 | Attrib3 | Attrib4 | Value

I need to export average, max, min value group by attrib elements, and I use following code:

        var queryTable = from rows in dataTable.AsEnumerable()
                         group rows by new
                         {
                             Attrib1 = rows["Attrib1"],
                             Attrib2 = rows["Attrib2"],
                             Attrib3 = rows["Attrib3"],
                             Attrib4 = rows["Attrib4"]
                         } into grp
                         select new
                         {
                             Attrib1 = grp.Key.Attrib1,
                             Attrib2 = grp.Key.Attrib2,
                             Attrib3 = grp.Key.Attrib4,
                             Attrib4 = grp.Key.Attrib14,
                             Avg = grp.Average(s => Convert.ToDouble(s["Value"])),
                             Min = grp.Min(s => Convert.ToDouble(s["Value"])),
                             Max = grp.Max(s => Convert.ToDouble(s["Value"])),
                             Count = grp.Count()
                         };

If I need also to export one IDstring (not necessary all occurrence) that match max and min value, how can I do it?

I have tried with another linq query for every max and min element of upon querytable results to the original datatable but it is too slow for the number of elements I have. Can you help me please?

Answer 1

With the big help of coder of code, this could be the solution: First I make on order by Value and then i take first and last element.

        var queryTable = from rows in resultTable.AsEnumerable()
                         orderby rows.Field<double>("Value")
                         group rows by new
                         {
                             Attrib1 = rows["Attrib1"],
                             Attrib2 = rows["Attrib2"],
                             Attrib3 = rows["Attrib3"],
                             Attrib4 = rows["Attrib4"]
                         } into grp
                         select new
                         {
                             Attrib1 = grp.Key.Attrib1,
                             Attrib2 = grp.Key.Attrib2,
                             Attrib3 = grp.Key.Attrib3,
                             Attrib4 = grp.Key.Attrib4,
                             Avg = grp.Average(s => Convert.ToDouble(s["Value"])),
                             Min = grp.Min(s => Convert.ToDouble(s["Value"])),
                             IDStringMin = grp.First().Field<string>("IDstring"),
                             Max = grp.Max(s => Convert.ToDouble(s["Value"])),
                             IDStringMax = grp.Last().Field<string>("IDstring"),
                             Count = grp.Count()
                         };