How to show the field value based on other aggregate field

[Su]

Hi,
I am creating the report with standalone designer. 
My sample datasource will be like this below,

Data Source
-----------
Name,QtyValue,DateTime
S001,100,2018-05-01
S001,200,2018-05-02
S001,300,2018-05-03
S001,50,2018-05-04
S001,250,2018-05-05
S001,100,2018-05-06
S002,200,2018-05-02
S002,30,2018-05-04
S002,100,2018-05-05

In my report group footer, I would like to display the 
Maximum/Minimum Qtyvalue and the DateTime value for that maximum value. 
I tried to use the expression 
IIF(Fields.QtyValue =  Max(Fields.QtyValue), Fields.DateTime, "")

It didn't work. Can you guys please advise me how to achieve.

Expected
---------
Name: S001

Max                                        Min
Value         Date                     Value            Date
300            2018-05-03          50                 2018-05-04


Actual
-------
Name: S001
Max                                Min
Value  Date                    Value          Date
300                                 50              

Thanks in advance. 

[Todor]

Hello Su,

The requirement to display the DateTime when the QtyValue is max/min in the GroupFooter section can be achieved with a Custom Aggregate, i.e. a User Aggregate Function (lets say for the max GetValueForMaxValue) that receives as arguments Fields.QtyValue and Fields.DateTime, finds the max/min of the QtyValue while aggregating along the group values, and returns the corresponding DateTime.
The expression in the report will look like:

= GetValueForMaxValue(Fields.DateTime, Fields.QtyValue)

I have attached a sample (CustomAggregate) demonstrating this approach.
Note that the assembly containing the custom aggregate functions (CustomAggregates.dll) should be copied to the folder of the Standalone designer - (Telerik Reporting installation folder)\Report Designer (for example C:\Program Files (x86)\Progress\Telerik Reporting R2 2018\Report Designer), and registered in its configuration file (Telerik.ReportDesigner.exe.config) as explained in the Extending Report Designer article.


Another approach is to display the max/min group values in the Detail instead of GroupFooter section. The max/min for the corresponding group can be taken using the scope of the group, i.e.

=IIF(Fields.QtyValue = Exec('group', Min(Fields.QtyValue)), "Min: " + Fields.QtyValue + ", Date: " + Fields.DateTime, "")

This approach is demonstrated in the attached MinMaxSample report.

Regards,
Todor
Progress Telerik