Remove figure from the second code....as you have used figure, it is opening a new figure.
File2=csvread('secondhalf.CSV')
% samplmean=mean(File2)
% std(File2)
averageY2 = mean(File2);
sigmaY2 = std(File2);
x1 = linspace(min(File2),max(File2),50); %this produces a sorted vector over which to plot the pdf
norm = normpdf(x1,averageY2,sigmaY2);
figure;
plot(x1,norm,'-k');
hold on;
File1=csvread('firsthalf.CSV')
averageY = mean(File1);
sigmaY = std(File1);
x = linspace(min(File1),max(File1),50); %this produces a sorted vector over which to plot the pdf
norm = normpdf(x,averageY,sigmaY);
plot(x,norm,'-k');
