MATLAB: Plot multiple errorbars in pairs

barbar centerserrorbarsxoffset

Hi again,
I have plotted some errorbars using the commands you suggested in my previous question:
x=1; y=8.35;
sd=4.13;
bar(x,y);
hold on
errorbar(x,y,sd)
ylim([0 14])
xticks([0:2])
hold off
However, I am trying to do the same with a pair of graphs, so in each number there are two bars instead of 1. I modified the code like this:
error=[3.3 2.1;1.1 4];
x=[1:2 ;1:2]'; 
y=[3.5 2.2; 5.2 3.3];
bar(x,y)
hold on
errorbar(x,y,error,'*')
ylim([-8 18])
xticks([1:2])
hold off
The problem is that the error bars which show the deviation don't fit exactly at the barcharts. Do you know how to fix this?
I have attached a screenshot

Best Answer

To locate the center of each grouped bar, use the undocumented bar object property, "XOffset" which is the horizontal offset of each bar-center from the group index value.
xCnt are the bar centers. 
error=[3.3 2.1;1.1 4];
x=[1:2 ;1:2]'; 
y=[3.5 2.2; 5.2 3.3];
h = bar(x,y)
hold on
% Get bar centers
xCnt =  h(1).XData.' + [h.XOffset]; 
% Alternative: xCnt = get(h(1),'XData').' + cell2mat(get(h,'XOffset')).'; % XOffset is undocumented
errorbar(xCnt(:),y(:),error(:),'*')  % <--- If you want 1 errorbar object
% errorbar(xCnt,y,error,'*')         % <--- If you want separate errorbar objects, 1 for each bar-group
% errorbar(...,'k*') to make the errorbars black (which is better than yellow)
ylim([-8 18])
xticks([1:2])
hold off
Related Question