Add error bars to grouped bar plot in MatLab

Question

I have a simple, grouped bar plot. I'm trying to plot the error bars, too, but I can't seem to figure it out.

I'm not too great with for loops, but I don't know if that's the only solution to this, or if I can just add another line of code to plot the error bars.

Here's my code and graph:

% Plot raw data
y = [316.45 292.14 319.96; 305.59 287.99 295.21]  % first 3 #s are pre-test, second 3 #s are post-test
err = [13.12 5.67 12.36; 12.43 6.83 11.67]

box on

bar(y)
set(gca,'xticklabel',{'Pre-test'; 'Post-test'}) 
ylim([200 360])
ylabel('RT (ms)')
xlabel('Session')

Answer 1

Here is a solution using the standard errorbar and bar functions. bar plots each group at the same x position, and uses the Xoffset property to shift the bars in a group. You can use the x position and Xoffset to plot the errorbars.

% Data
y = [316.45 292.14 319.96; 305.59 287.99 295.21]  % first 3 #s are pre-test, second 3 #s are post-test
err = [13.12 5.67 12.36; 12.43 6.83 11.67]

% Plot
figure(1); clf; 
hb = bar(y); % get the bar handles
hold on;
for k = 1:size(y,2)
    % get x positions per group
    xpos = hb(k).XData + hb(k).XOffset;
    % draw errorbar
    errorbar(xpos, y(:,k), err(:,k), 'LineStyle', 'none', ... 
        'Color', 'k', 'LineWidth', 1);
end

% Set Axis properties
set(gca,'xticklabel',{'Pre-test'; 'Post-test'});
ylim([200 360])
ylabel('RT (ms)')
xlabel('Session')