error bars in bar plot with categories

Hello

I have a bar plot with 3 categories where I want to insert error bars.

I've been trying it for a long time, but I can't find the solution.

x are the categories

y the values

errorplus and errorminus the errors values.

Can someone hel me?

Thank you very much!

x=categorical({'Hip';'Knee';'Ankle'});
y=[21.0416,19.5461,50;30.003601074218750,24.056737899780273,50;22.604316711425780,26.007211685180664,35];
errorplus=[0.434635639190674,1.783290743827820,0;1.722714424133301,1.000267505645752,0;0.471254885196686,2.722285032272339,0];
errorminus=errorplus;
figure;
bar(x,y);
title('Range of Motion','FontSize',18)
ylabel('Angle Values [°]','FontSize',18)
set(gca,'linewidth',2,'FontSize',14)
ylim([0 60]);

Answer 1

[Star Strider]

This seems to be an XOR situation. Apparently, it is possible to have categorical x-values or errorbar bars but not both.

This requires non-categorical x-values, although it produces the appropriate final result:

x=categorical({'Hip';'Knee';'Ankle'});
y=[21.0416,19.5461,50;30.003601074218750,24.056737899780273,50;22.604316711425780,26.007211685180664,35];
errorplus=[0.434635639190674,1.783290743827820,0;1.722714424133301,1.000267505645752,0;0.471254885196686,2.722285032272339,0];
errorminus=errorplus;
figure;
bar(x,y);
hBar = bar(y, 0.8);                                                     % Return ‘bar’ Handle
for k1 = 1:size(y,2)
    ctr(k1,:) = bsxfun(@plus, hBar(k1).XData, hBar(k1).XOffset');       % Note: ‘XOffset’ Is An Undocumented Feature, This Selects The ‘bar’ Centres
    ydt(k1,:) = hBar(k1).YData;                                         % Individual Bar Heights
end
hold on
errorbar(ctr, ydt, errorplus, '.r')                                     % Plot Error Bars
hold off
title('Range of Motion','FontSize',18)
ylabel('Angle Values [°]','FontSize',18)
set(gca,'linewidth',2,'FontSize',14)
ylim([0 60]);
set(gca,'XTickLabel',x)

producing this plot:

Answer 2

[Paul Himsl]

WOW .. thank you yery much!

Is it possible to "write" the values of each bar on the top of the bar when there are error bars already?

[Star Strider]

As always, my pleasure!

Working on it.

I had yet another R2019b Update failure (this time Update #3), so I have to uninstall and reinstall MATLAB, then try the Update again. This should be resolved in an hour or two. I apologise for the unavoidable delay.

[dpb]

"Is it possible to "write" the values of each bar on the top of the bar when there are error bars already?"

Showing how to write text is the link I posted; to add them as well as the error bars just adjust the y position to add the error value to the y value (for above) or subtract for below.

[Star Strider]

Finally ... reinstalled and updated!

To add the values of each bar at the top, the loop changes to:

for k1 = 1:size(y,2)
    ctr(k1,:) = bsxfun(@plus, hBar(k1).XData, hBar(k1).XOffset');       % Note: ‘XOffset’ Is An Undocumented Feature, This Selects The ‘bar’ Centres
    ydt(k1,:) = hBar(k1).YData;                                         % Individual Bar Heights
    for k2 = 1:size(ydt,2)
        text(ctr(k1,k2), ydt(k1,k2)+errorplus(k1,k2), sprintf('%.1f', ydt(k1,k2)), 'HorizontalAlignment','center','VerticalAlignment','bottom');
    end
end

The inner loop is necessary in order to plot the values correctly.

Make appropriate changes to get the result you want.

Answer 3

[dpb]

This is a royal pain for even numeric axes; even worse for categorical. Complain to TMW about the sorry quality of implementation for bar to not provide the necessary tools <See LINK for example w/ numeric axis> and then errorbar hasn't been enhanced to allow categorical variables on x-axis...besides, there's no concept of a fractional value for a categorical variable to let you move to the right bar position for the grouped bars. All in all, it's a royal mess of not being a complete packaged solution. Disgraceful in my opinion.

Anyway, only practical way I see is to actually plot the figure as numeric underlying data and then label the result as desired...

...    % your preliminaries here...
figure;
hB=bar(double(x),y);                            % create the bar as numeric instead of categorical x axis
title('Range of Motion','FontSize',18)
ylabel('Angle Values [°]','FontSize',18)
set(gca,'linewidth',2,'FontSize',14)
ylim([0 60]);
hold on
                                               % get ready to put the errorbar() on top...
err=errorplus;                                 % all errors were same +/- so  use symmetric                                               
hEB=[];                                        % placeholder of the errorbar object handles
hT=[];                                         % ditto text handles
for i=1:numel(hB)                              % put the errorbar on each bar
  hEB=[hEB; errorbar(hB(i).XData+hB(i).XOffset,hB(i).YData, err(:,i),'.k')];
  hT=[hT text(hB(i).XData+hB(i).XOffset, ...
              hB(i).YData+err(:,i).', ...
              num2str(hB(i).YData.','%.2f'), ...
             'VerticalAlignment','bottom','horizontalalign','center','fontsize',9)];
end
xticklabels(categories(x))                     % label the ticks by categorical names

There really should be built in facilities inside bar for adding annotations w/o relying on hidden properties and so much coding.

Hadn't previously thought of the limitation in errorbar, but it should be enhanced, too, and then the dificulties in mixing the internals of a categorical axis with positions other than exactly at the category values should be addressed as well. So much work to do that TMW never seems to want to address but that would be major boosts in overall productivity to quit having to spend hours trying to find workarounds. :(

[dpb]

Essentially same workaround as S-S's but slightly more compact.

However, his line w/ bsxfun adding hBar.Xdata,hBar.XOffset fails on R2017b here on no method implemented to add a categorical and double. Not sure which release he's on as to when that restriction removed.

To do that, with a categorical axis didn't work w/out double(hBar.XData) but then errorbar failed on categorical x axis by always rounding to the integer value and drawing all points at the middle bar.

Looks like at least some of the issues may have been partially addressed, but still not fully integrated.

[dpb]

Above produces

Didn't delve into other solution enough to see why it took the second loop; perhaps didn't think to index into the error array by column to retrieve the array corresponding to the YData vector.

[Star Strider]

The second loop is necessary for the text call in order to plot the correct strings in the correct places. I tried it first without the second loop, and only added it because it proved to be necessary.

[dpb]

Above looks ok w/o double loop to me???

HMMM...yours is Hip/Knee/Ankle whereas default order is Ankle/Hip/Knee, the order of categories of x in alphabetic order. Mayhaps there's the difference.

The data are the same for both, however, just the order of them on the x axis.

>> figure
>> bar(x,y)

results in

which is order in which OP defined the arrays. Not sure what changed the axis order in yours.

Could it be version, perhaps? Mayhaps the newer release honors the array order instead of the alphabetic of R2017b as categories here shows? What does the following return on your system (R2019 I think?)

>> x
x = 
  3×1 categorical array
     Hip 
     Knee 
     Ankle 
>> categories(x)
ans =
  3×1 cell array
    {'Ankle'}
    {'Hip'  }
    {'Knee' }
>> double(x)
ans =
     2
     3
     1
>> 

[dpb]

Ah-so! I hadn't seen you threw away the bar(x,y) call by the subsequent hBar=bar(y,0.8) so the x values weren't provided to the bar object explicitly. That 'splains it all and why it took the second level addressing.

Answer 4

[Paul Himsl]

Thank you all very much for your help!

[dpb]

Glad to help where TMW falls short...

BTW, the route S-S took can also be done w/o the double loop; just have to recognize the order is different as noted in previous comment--the following generates identical plot.

hB=bar(y);         % the y data versus column number instead of ordered categorical x
ylim([0 60]);
hold on
hEB=[];            % placeholder of the errorbar object handles
hT=[];             % ditto text handles
for i=1:numel(hB)
  hEB=[hEB; errorbar(hB(i).XData+hB(i).XOffset,hB(i).YData, err(:,i),'.k')];
  hT=[hT text(hB(i).XData+hB(i).XOffset, ...
              hB(i).YData+err(:,i).', ...
              num2str(hB(i).YData.','%.2f'), ...
              'VerticalAlignment','bottom','horizontalalign','center','fontsize',9)];
end
xticklabels(cellstr(x))  % label in numeric, not alphabetic order

BTW, hEB, hT are the handles to the errorbar and text objects saved so can make additional tweaks on their properties should such be desired...