# How to add percent change in barplot?

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Daphne PARLIARI on 4 Jan 2021
Commented: Daphne PARLIARI on 4 Jan 2021
Hello everyone and happy new year!
I have a barplot (average deaths per degree of temperature, 30-37oC) to which I want to add the percentage change from bar to bar. Attached you can find the excel file I am proccessing and here is the part of code that produces tha barplot.
Is there an efficient way to do so?
PS. I am on R2019a.
idx = Daily_Data.Daily_T(:) > 30;
Daily_Data_new = Daily_Data(idx,:);
[G, Temperature] = discretize(Daily_Data_new.Daily_T, 30:37);
d_mean = accumarray(G, Daily_Data_new.Daily_Deaths, [length(Temperature), 1], @mean);
bar(Temperature, d_mean); xlabel('T (oC)'); ylabel('Average deaths');

Steve Eddins on 4 Jan 2021
Edited: Steve Eddins on 4 Jan 2021
If you want text labels instead of a line plot (Cris' suggestion), then try this code. It gets the Bar object as the output argument from bar, and then computes the percent change and where to put the labels using the XData and YData properties of the Bar object.
b = bar(Temperature, d_mean); xlabel('T (oC)'); ylabel('Average deaths');
x = b.XData;
y = b.YData;
percent_change = 100 * diff(y) ./ y(1:end-1);
for k = 1:length(percent_change)
text(x(k+1),y(k+1),sprintf('%0.1f%%',percent_change(k)),...
'HorizontalAlignment','center',...
'VerticalAlignment','bottom')
end
Daphne PARLIARI on 4 Jan 2021
With this code below
x = b.XData;
y = b.YData;
reference_temp = y(1); % 30oC in plot
percent_change = 100 * (y - reference_temp) / reference_temp;
for k = 1:length(percent_change)
text(x(k+1),y(k+1),sprintf('%0.1f%%',percent_change(k)),...
'HorizontalAlignment','center',...
'VerticalAlignment','bottom')
end
I am getting the Error: Index exceeds the number of array elements (8).

Cris LaPierre on 4 Jan 2021
You can add a line plot to a bar plot. Just use the hold on command.
If you need it to be on a separate Y scale, look at this example
Daphne PARLIARI on 4 Jan 2021
Thank you Cris! Since I am not very experienced in MatLab, Steve's answer was easier for me to comprehend...