how to hide the duplicte rows in datatable in asp.net using

Question

 My code as follows
 
  to what extent was this course userful    Dropdownlist1 (Good,Fair,Poor)


 When i  select the Poor from the Dropdownlist1 the popup will be shown as follows.


    POPUP  as follows

    Negatuve_Feedback
    textbox1(in that textbox1 type the reason for poor)
    OK Button)


 When i click the OK (Button) selected dropdown and reason for poor is displayed in to the Gridview.


  Gridview as follows


    Dropdown   Reason

      0                 not good


suppose if user wrongly type the reason for poor, user select the Dropdowlist1  and select the poor then popup screen will be displayed, then in the textbox1 type the reason and click the ok button.


 Then in the gridview two reason has been displayed as follows

    Gridview as follows


    Dropdown   Reason

      0                 not good    (Old Reason)
      0                 the student performance is not good at all this month  (New Reason)



i want to hide the Old Reason in the gridview, when user tyoe the reason in the textbox1 second time.

i want to hide the First Row in the gridview.

for that how can i do using csharp.

Regards,
narasiman P