MATLAB: Does the COLORBAR function create a new color bar when I want to only update the existing color bar

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When I create an image and a color bar as follow,

hi = imagesc(rand(256, 256));
hc = colorbar('peer', gca,'EastOutside','position',[0.1 0.05 0.02 0.8]);

and then change the range of my data using the command,

set(hi, 'CData', 200*rand(256,256));

and try to update the color bar using the command,

hc = colorbar('peer', gca,'EastOutside','position',[0.1 0.05 0.02 0.8]);

a new color bar is place on top of the old one. I expected the color bar to be updated.

Best Answer

We have verified that there is a bug in MATLAB 7.0.4 (R14SP2) in the way that the COLORBAR function checks for existing color bars with user-defined position vectors.

To work around this issue, save the handle of the color bar you wish to update or replace. When you are ready to update the color bar, delete the color bar and create a new color bar. For example,

hi = imagesc(rand(256, 256));
hc = colorbar('peer', gca,'EastOutside','position',[0.05 0.1 0.015 0.8]);
set(hi, 'CData', 200*rand(256,256));
delete(hc);
hc = colorbar('peer', gca,'EastOutside','position',[0.05 0.1 0.015 0.8]);

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MATLAB: Edit colorbar of heatmap (string)

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'})

MATLAB: How to remove the Range from colorbar in HeatMap

Heatmaps are notoriously difficult to customize outside of the HeatmapChart Properties. The only property that I'm aware of that affects the heapmap colorbar is the ColorbarVisible property that just turns the colorbar on/off and resizes the heatmap accordingly.

One alternative is to use imagesc() instead which gives you full access to the colorbar and many other properties.

If you'd like to stick with a heatmap, here's a workaround that puts a customizable colorbar on top of the existing heatmap colorbar.

% Create the heatmap with a heatmap-colorbar
fh = figure();         % We'll use the figure handle.
clf()
data = randi(3,8,8)-1; 
data(logical(eye(8))) = NaN; 
hm = heatmap(data);    % We'll use the heatmap output object.
colormap([1 0 0; 1 1 0; 0 1 0])
% Put an axis over top of the heatmap
% The axis will not be visible but will cover all area 
% to the right of the heatmap. 
hmp = hm.Position; 
cbax = axes('Position',[sum(hmp([1,3])), 0, 1-sum(hmp([1,3])), 1],...
    'XTick',[], 'YTick', [], 'Color',fh.Color);
cbax.XAxis.Visible = 'off';
cbax.YAxis.Visible = 'off';
% Set the new axis color map to match the 
% heatmap's colormap
cbax.Colormap = hm.Colormap; 
% Add a colorbar the same vertical position as the heatmap
cbh = colorbar(cbax,'Position',[.90, hmp(2), .03, hmp(4)]); 
% Set the limits to 0:1 and set the ticks so that they 
% are in the center of each bar
cbh.Limits = [0,1]; 
nColors = size(hm.Colormap,1); 
cbh.Ticks = (1/nColors : 1/nColors : 1) - 1/nColors/2; 
% Set the new labels for each tick
cbh.TickLabels = 0:nColors-1; 
% Set the colorbar fontsize to the same value as heatmap fontsize
cbh.FontSize = hm.FontSize;

Note that the NaN values are no longer represented in the new colorbar.

Best Answer

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