How to make two global field power figures in the same figure?

if length(size(EEG.data))==3
   gfp = std(mean(EEG.data,3));
end
figure;
plot(EEG.times, std(mean(EEG.data,3)), 'r', 'linewidth', 3);

I am trying to use the above codes for GFP calculation, but I have two conditions. I want to GFP of two conditions in the same figure, so it is much easier for me to make comparison for difference.

I tried to load only two datasets and use ALLEEG, but failed. Can you help share any suggestions to me? Many thanks.

gfp = std(mean(ALLEEG.data,3));