MATLAB: Heatmap Chart – Depict Squares rather than Rectangles

Question

Hey guys,

I have a heatmap object h and would like to depict squares rather than rectangles (see appendix). The heatmap properties (https://de.mathworks.com/help/matlab/ref/matlab.graphics.chart.heatmapchart-properties.html) do not provide any help.

Do you have an idea?

Thank you very much!

Answer 1

It drives me nutz that heatmap properties are special cases. To set the aspect ratio of the heatmap, you need to adjust the axis or figure size based on the number or rows & columns. Below are two functional demos. The first adjusts the axis size and recenters it. The second adjusts the figure size instead. I recommend the first method so the heatmap title and other graphics won't potentially expand beyond the figure boundaries.

Method 1: Adjust axis size and re-center

% Create heatmap using built-in Matlab data

load patients
tbl = table(LastName,Age,Gender,SelfAssessedHealthStatus,...
    Smoker,Weight,Location);
h = heatmap(tbl,'Smoker','SelfAssessedHealthStatus');
% Temporarily change axis units 
originalUnits = h.Units;  % save original units (probaly normalized)

h.Units = 'centimeters';  % any unit that will result in squares

% Get number of rows & columns

sz = size(h.ColorData); 
% Change axis size & position;
originalPos = h.Position; 
% make axes square (not the table cells, just the axes)

h.Position(3:4) = min(h.Position(3:4))*[1,1]; 
if sz(1)>sz(2)
    % make the axis size more narrow and re-center
    h.Position(3) = h.Position(3)*(sz(2)/sz(1)); 
    h.Position(1) = (originalPos(1)+originalPos(3)/2)-(h.Position(3)/2);
else
    % make the axis size shorter and re-center
    h.Position(4) = h.Position(4)*(sz(1)/sz(2));
    h.Position(2) = (originalPos(2)+originalPos(4)/2)-(h.Position(4)/2);
end
% Return axis to original units
h.Units = originalUnits; 

Method 2: Adjust figure size

% Create heatmap using built-in Matlab data
load patients
tbl = table(LastName,Age,Gender,SelfAssessedHealthStatus,...
    Smoker,Weight,Location);
h = heatmap(tbl,'SelfAssessedHealthStatus','Smoker');
%                ^^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^    switched from method 1
% Temporarily change figure units 
fh = gcf();  %if you don't already have the figure handle
originalUnits.fig = fh.Units;  % save original units (probaly normalized)
originalUnits.ax = h.Units; 
fh.Units = 'centimeters';  % any unit that will result in squares
h.Units = 'Normalize'; 
% Get number of rows & columns
sz = size(h.ColorData); 
% make axes square (not the table cells, just the axes)
h.Position(3:4) = min(h.Position(3:4))*[1,1]; 
fh.InnerPosition(3:4) = min(fh.InnerPosition(3:4))*[1,1]; 
% Change figure position;
if sz(1)>sz(2)
    % make the figure size more narrow
    fh.InnerPosition(3) = fh.InnerPosition(3)*(sz(2)/sz(1)); 
else
    % make the figure size shorter
    fh.InnerPosition(4) = fh.InnerPosition(4)*(sz(1)/sz(2)); 
end
% return original figure units
fh.Units = originalUnits.fig; 
h.Units = originalUnits.ax;