Little tricky -- although in a recent release TMW finally made the
XEndPoints
property visible so at least can see it is there...although need to have a klew about how the grouped bar is drawn to be able to understand what really need -- and the documentation isn't at all good in that regards. The only example is a trivial one of a regular simple one-series bar plot. My (long-running) ranting about the shortcomings of bar() aside,
yyaxisleft;
hB=bar(x,a);
ylim([0 40]);ylabel('time/s')
holdon
hEB=errorbar(hB(1).XEndPoints,hB(1).YEndPoints,hB(1).YEndPoints/50,'LineStyle','none');
yyaxisright;
hB=[hB;bar(x,b)];
ylim([0 2]);ylabel('mean/mm');ytickformat('%.1f')
holdon
hEB(2)=errorbar(hB(4).XEndPoints,hB(4).YEndPoints,hB(4).YEndPoints/50,'LineStyle','none');
xticklabels({'part 1','part 2'});
I arbitrarily used 1/50th the bar height for the error magnitudes; obviously you'll use your own values in lieu thereof.
NB: bar() creates two handles here (one for each group) with each call so the first handle you want is the first for the LH group data and then the last for the RH group with the "real" data values.
You could, of course, use the a(:,1), b(:,2) values, but this shows how to save/retrieve data from the bar chart itself for the generic solution.
If it weren't for the need to put the errorbar on,
x=categorical({'part 1','part 2'});
hB=bar(x,a);
would get the xticklabels automagically, but then the x axes is a categorical axis and can't plot the explicit x positions for the errorbar -- they get rounded to the midpoint categorical tick location instead.
