Summarizing text field based on Group

I've a set of data which has 3 columns as Product Name, Quantity and Narration. and I've grouped the records based on Product Name. So I can easily get the Product Name and Total Quantity. But issue is when have to get the Summery of Narration Field.

I've arranged the field name in the Group Footer. I tried a formula like

WhileReadingRecords;

StringVar ds_narr;

ds_narr := ds_narr + //Iif( InStr(ds_narr,' '+Trim({Command.NARR}))>0, '',

Iif(Trim(ds_narr)='','',chr(10)) + ' '+Trim({Command.NARR}) ;

But in this data is getting appending continuously. It's not getting Summarized Based on Product Name.

For Ex: if

A,50,'Narr1'

A,100,'Narr2'

B,50,'Narr3''

Result:

A,150,'Narr1,Narr2' --> Correct

B,50,'Narr1,Narr2,Narr3' --- Wrong

Please help.