How can i reset a plotted line everytime I draw a new one?

Hi, a big novice when using matlab and i've been using guide to create a gui. In my gui i wish to have a pop-up menu which can plot lines of the selected data on the axis. I've gotten this to work, my issue is each time i select a new feature on the drop down it merely draws a new line and keeps the old ones. Is there a way to maybe add a limit to the amount of lines drawn on the axes, which when you draw a new one after the limit, the first line is replaced?

At the moment my code is just a simple switch case:

 function popupmenu1_Callback(hObject, eventdata, handles)
% hObject    handle to popupmenu1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: contents = cellstr(get(hObject,'String')) returns popupmenu1 contents as cell array
%        contents{get(hObject,'Value')} returns selected item from popupmenu1
contents = get(handles.popupmenu1,'Value');
num =  get(handles.bigbox,'UserData');

switch contents

         case 1
             n = 1;

         case 2 
             n = 2;

         case 3
              n = 3;

         case 4
              n = 4;

         case 5
              n = 5;

         case 6
              n = 6;

         case 7
              n = 7;

         case 8
              n = 8;

         case 9
              n = 9;

         case 10
              n = 10;

         case 11
              n = 11;

         case 12
              n = 12;

         case 13
              n = 13;

         case 14
              n = 14;

         case 15
              n = 15;

         case 16
              n = 16;

         otherwise
              n = 17;             

end

t = num(n,4):4:num(n,5);
y = 10.^(num(n,1) - (num(n,2)./(num(n,3) + t)));
line(t,y);

Not part of this question but also, if there would be a way to make that a bit more condensed information would be greatly appreciated. Also a way of making each line a different colour would be good! :)

Sorry if this is a newbie question and the answer is somewhere inside the matlab help, i've tried looking and found no solution.

Answer 1

[Sara]

Before plotting the new variable:

delete(fig_handle)

and replace the last line in your code with:

fig_handle = line(t,y);

You can also eliminate the switch with:

if contents < 17
   n = contents;
else
   n = 17;
end