Edit colorbar of heatmap (string)

Hi,

Is it possible to edit the colorbar of a heatmap such that it looks like the following image (rapidly created with paint ;) )

So the values aren't numeric but strings.

Thanks for help!

[Adam Danz]

The handle to the colorbar in heatmap is inaccessible. Without the handle, you can't change properties to the colorbar; you can't even delete it. Even when you try to add a new colorbar, you cannot output the handle with a heatmap plot.

heatmap() in general is highly restrictive in the user's abilty to manipulate many of its properties. I used to use heatmap more frequently prior to these changes and have moved onto using imagesc() instead. Bummer.

Answer 1

[Adam Danz]

This can't be done with heatmap() (see comments under the question).

If you're using a different function that allows access to the colobar, it's fairly straightforward. Here's a demo.

% Create demo
C = rand(3,4)/10; 
imagesc(C)
cbh = colorbar(); 

% set color range
caxis([0,.1])

% set ticks 
set(cbh, 'YTick', [0.001, 0.01, 0.05, .1], ...
    'YTickLabel', {'p=0.001', 'p=0.01', 'p=0.05', 'p=.1'})

Answer 2

[Christian Karcher]

The handle to the colorbar is accessible, and with it all modifications:

figure; 
heatmap(rand(5))
axs = struct(gca); %ignore warning that this should be avoided
cb = axs.Colorbar;
cb.TickLabels = {'p<0.1','p>0.1','...'};

[Adam Danz]

You can't assign the tick labels without first assigning the ticks.

[Christian Karcher]

well... you can?

It just replaces the automatically generated ticks from the heatmap. It's a working minimal example, feel free to copy & paste it into matlab and see for yourself.

If you want to have specific tick replacement, of course you should re-define the ticks first, but it should really just be a minimal example, not a full customizable colorbar wondertool ;)

[giannit]

many thanks! this should be the accepted answer

[Alexander Krauss]

Dear Christian,

is it also possible to set the colorbar to a percent scale?

I know it works for standard colormaps, but I don't know whether you can change it in a heatmap.

Would be very glad if you could help me out. :)

Best regards,

Alex

[Christian Karcher]

I am not aware of an option to directly format a value to percentage.

But the ticks can be directly reformated. So it would be a two-stage process:

1. multiply your data by 100
2. add a percent sign to the labels

figure; 
heatmap(rand(5)*100);  % convert data to percent
axs = struct(gca); %ignore warning that this should be avoided
cb = axs.Colorbar;
cb.Ruler.TickLabelFormat = '%g%%'; % add percent sign to labels

See https://de.mathworks.com/help/matlab/matlab_prog/formatting-strings.html for all your formatting needs.

[Alexander Krauss]

Great solution, thanks a lot (also for the rapid reply) ! :)

Best regards,

Alex

[Muhanned Alsaif]

another way to access the colorbar can be found in the following post:

https://www.mathworks.com/matlabcentral/answers/654008-axis-ticks-and-colorbar-labels-in-bold-heatmap

Answer 3

[Tony Castillo]

Is it possible to add a label to that colour bar which is directly created in a heatmap? I mean we can tag a SURF plot (the colourbar because it is separated from the surfplot), but I have not found the manner of doing the same in the colorbar of the heatmap.