How to plot correctly errorbars on grouped bar plot?

Hello everyone,

I am using a livescript to present some data.. data is a 4x7 matrix, so nbars is 4, ngroups is 7

figure
labels = categorical({'Mental Demand' 'Physical Demand' 'Temporal Demand' 'Performance', 'Effort', 'Frustration', 'Overall'});
b=bar(labels',data');
title('RAW NASA TLX');
box off
hold on
% Calculate the number of groups and number of bars in each group
[ngroups,nbars] = size(data');
% Get the x coordinate of the bars
x = nan(nbars,ngroups);
for i = 1:nbars    
    x(i,:) = b(i).XEndPoints;
end
% Plot the errorbars
errorbar(x',data',error','k','linestyle','none');
hold off


legendText = cell(1, numel(A));
for i = 1:numel(A)
    cameraType = A{i};
    legendText{i} = cameraType;
end

legend(legendText);

The resulting plot in the livescript is wrong: all the errorbars are in the center of each of the respective group

But if I put the same code in the command window the plot is correct

Can you explain me what is going on?

I am sure that I am doing something wrong but I can not understand why (I took the errorbar part from some code online, it seems right to me but idk...)

Answer 1

[Voss]

I am able to reproduce the problem; it looks like a bug in MATLAB, having to do with creating an errorbar in an axes that has a categorical x-axis, within a live script context.

A workaround is to use a numeric x-axis instead of categorical. Something like this (I've run this same code in a live script, and it produces the same result):

% random data, for demonstration:
data = 20+80*rand(4,7);

% random error, for demonstration:
err = 25*rand(4,7); % don't use "error" as a variable name, since it's a built-in function name


figure
labels = categorical({'Mental Demand' 'Physical Demand' 'Temporal Demand' 'Performance', 'Effort', 'Frustration', 'Overall'});

% number of groups:
ngroups = size(data,2);

% create the bars, using integers instead of categorical labels
b = bar(1:ngroups,data);

% set the x-ticks and x-tick labels:
xticks(1:ngroups)
xticklabels(labels)

title('RAW NASA TLX');
box off
hold on

% Get the x coordinate of the bars (a shorter way)
x = get(b,'XEndPoints');
x = vertcat(x{:});

% Plot the errorbars
errorbar(x,data,err,'k','linestyle','none');
hold off

Note that the groups there are in the order you specified in labels, which is not the case by default when using a categorical x-axis (as in your example, they're sorted alphabetically). If you want the groups to be in alphabetically-sorted order, you can do this:

figure
labels = categorical({'Mental Demand' 'Physical Demand' 'Temporal Demand' 'Performance', 'Effort', 'Frustration', 'Overall'});

% number of groups:
ngroups = size(data,2);

% sort the labels into alphabetical order:
[sorted_labels,sort_idx] = sort(lower(labels));

% create the bars, using integers instead of categorical labels
b = bar(1:ngroups,data(:,sort_idx));

% set the x-ticks and x-tick labels:
xticks(1:ngroups)
xticklabels(sorted_labels)

title('RAW NASA TLX');
box off
hold on

% Get the x coordinate of the bars (a shorter way)
x = get(b,'XEndPoints');
x = vertcat(x{:});

% Plot the errorbars
errorbar(x,data(:,sort_idx),err(:,sort_idx),'k','linestyle','none');
hold off

[Marianna Pizzo]

Thanks for the help :) Probelm solved

[Voss]

You're welcome!