Update legend to current plot

I'm writing a code where I have one constant dataset that stays in the plot the entire time while the other datasets pop up in the plot one by one.(I'm deleting the pop-up dataset-plot after every iteration; which means that I at every time only have two plots in my figure - the constant dataset and the current pop-up dataset). As far as I know you can't have multiple legends in a matlab plot, so I want to make a legend for the pop-up datasets that updates after every iteration (i.e legend changing color in accordance to plot). To delete the plots i'm simply using the delete(plot) command however I haven't figured out if you can do anything similar with legends

Answer 1

[KSSV]

% constant plot 
 t = linspace(0,2*pi) ;
 x = 0.5*sin(t) ;

   for i = 1:100
       plot(t,x,'r') ;  % plot constant sine function
       hold on
       % Generating a random varying second function 
       dx = 0.1*randn(size(t)) ;
       x2 = x+dx ;     % A varying function
       plot(t,x2,'color',rand(1,3)) ; % plot second varying function
       hold off
       legend('sin function','varying function')
      drawnow
end