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How to set the x axis on heatmap

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Roberto P
Roberto P on 20 Mar 2020
Commented: Roberto P on 21 Mar 2020
Hi all, I'm trying to plot a heatmap, but I'm not able to set up the x axis properly.
I have a data set that I run through this code to obtain a 2D histogram (that's what I'm aiming for)
[M,N]=size(data);
xbin=[0:0.2:8];
[counts,l]=histcounts(data(1,:),xbin);
result=counts;
for i=2:M
[counts,l]=histcounts(data(i,:),xbin);
result=[result; counts];
end
Then I try to plot the heatmap with this
ybin=[1:31];
heatmap(result,'Xdata',xbin,'YData',ybin);
colormap jet
But I get the error that lenght of xbin doesn't match the lenght of result.
I know that the error it's because xbin values are edges and not centers, so I end up having 1 extra value on the xbin var. Do you know how I could set up the edges value on the x axis? Thanks.
A workaround could be using hist instead of histcounts, so the values of xbin will be centers and not edges, but I'd like to avoid this solution.

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Accepted Answer

Cris LaPierre
Cris LaPierre on 21 Mar 2020
You know the problem, you just have to decide what approach you want take. It's easy enough to use indexing to determine the points to use
heatmap(result,'Xdata',xbin(1:end-1),'YData',ybin);
If you do want to use the center point, try something like this
midpt = movmean(xbin,2,'Endpoints','discard');
heatmap(result,'Xdata',midpt,'YData',ybin);

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Roberto P
Roberto P on 21 Mar 2020
Thank you, that does the job perfectly. I've been trying to use histogram2, but with no results, probably because I didn't understand very well the input data and I constantly got an error message. That's why I ended up with heatmap, because was the only fuction that was giving me something close to what I was looking for.
I appreciate it, thanks.
Cris LaPierre
Cris LaPierre on 21 Mar 2020
One last comment then. I'm not sure if your y-values are important, but if you want them to match what you were getting with heatmap, use axis ij. The benefit is you don't have to use flipud.
...
h = histogram2("XBinEdges",xbin,"YBinEdges",ybin,"BinCounts",result');
axis ij
...
Roberto P
Roberto P on 21 Mar 2020
Yes, they are important. Thank you for the suggestion.

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More Answers (1)

Walter Roberson
Walter Roberson on 21 Mar 2020
[M,N]=size(data);
xbin=[0:0.2:8];
[counts,l]=histcounts(data(1,:), [xbin, inf]);
result=counts;
for i=2:M
[counts,l]=histcounts(data(i,:), [xbin, inf]);
result=[result; counts];
end

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