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I am trying to plot a heatmap as the following:
data = [2 1 0 0 0 0 0 0 0 0;1 2 15 0 0 0 0 0 0 0];
colormap('hot');
imagesc(data);
colorbar;
But I want a colorbar with only the values in my data. I don't really need the "transitioning" ones. Is there a way to do so?
Thanks!

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Kelly Kearney
Kelly Kearney 2016-1-16

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The unique values in you original question are [0 1 2 15]. Do you want just those to appear in the colorbar, or all possible integers between 0 and 15?
For the former:
data = [2 1 0 0 0 0 0 0 0 0;1 2 15 0 0 0 0 0 0 0];
[unq, ~, iunq] = unique(data);
iunq = reshape(iunq, size(data));
ncol = length(unq);
cmap = hot(ncol*2);
cmap = cmap(1:2:end,:);
imagesc(iunq);
colormap(cmap);
cb = colorbar;
set(gca, 'clim', [0.5 ncol+0.5]);
set(cb, 'ticks', 1:ncol, 'ticklabels', cellstr(num2str(unq)));
Walter's code covers the latter case. As a side note, I'd usually just suggest hot(4) to get the 4-color hot colormap, but interpolating hot to only 4 colors results in two nearly-identical shades of yellow; hence the doubling of colors and then using every other in my cmap generation above.

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Walter Roberson
Walter Roberson 2016-1-16
My code covers labeling only those values, but would generate the intermediate colors as well.
Speaking of intermediate colors, I would suggest that ncol be computed from max() and min() of the data, the colormap generated, and then indexed at the appropriate indices for the unique values. In that way the the colors would reflect relative values, whereas with your scheme, the colors only represent ordering of values.
Arthur Brigatto
Arthur Brigatto 2016-1-18
thanks for replying!
I am getting the following error: "The name 'ticks' is not an accessible property for an instance of class 'colorbar'."
Perhaps MATLAB version?
Arthur Brigatto
Arthur Brigatto 2016-1-18
Sorry, get it now! replaced ticks by ytick and tyckslabel by yticklabel and now it works. So far I have what I need! Thank you very much.
Kelly Kearney
Kelly Kearney 2016-1-19
The 'ticks', 'ticklabel' combo is necessary for HG2 (R2014b+). For earlier versions, substitute '[x/y]tick', '[x/y]ticklabel' as appropriate depending on colorbar orientation.
AASHNA SUNEJA
AASHNA SUNEJA 2020-10-29
Hi
I want my data [4.64 5.99 4.97 5.71 5.34 8.1 8.01 6.12 5.58 8.11 7.94 7.16 7.25 7.5 7.59] to be plotted in 15 equal regions of a circle. Each value to be represented by different color. How I can I do this? The code given above plots the values in a stairght line. For reference I am attaching a plot. A similar profile I want from my experiemntal values. Can anyone help me with this.

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Walter Roberson
Walter Roberson 2016-1-11

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data_range = ceil(max(data(:))) - floor(min(data(:))) + 1;
imagesc(data);
colormap(hot(data_range));
colorbar();

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Arthur Brigatto
Arthur Brigatto 2016-1-15
Perhaps I did not make myself clear. Plotting like this the colorbar displays values like [2 1.8 1.6 1.4 1.2 1 0.8...0]. I want only 2, 1 and 0.
Walter Roberson
Walter Roberson 2016-1-15
If you are using R2014b or later see http://www.mathworks.com/help/matlab/ref/colorbar.html#bt56gkg
For MATLAB R2014a and earlier, colorbar() creates a new axes, which you can record the handle of and set() the YTick parameter of.
You would probably want to be setting the ticks at unique(data(:))

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