% preallocate default values
pks1 = nan(25,1);
loc1 = nan(25,1);
width1 = zeros(25,1);
prom1 = nan(25,1);
for i=1:25
[tmp_pk, tmp_loc, tmp_width, tmp_prom]= findpeaks(XmRNA(:,i),t);
% if peak is found, update values with the *first* peak
if ~isempty(pks)
pks(i) = tmp_pk(1);
loc1(i) = tmp_loc(1);
width1(i) = tmp_width(1);
prom1(i) = tmp_prom(1);
end
end
you should think about whether you want the first peak or a different one (e.g., the most prominent peak)
Note: may be worth checking speed of parfor
