How to set the x axis on heatmap

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.

Answer 1

[Cris LaPierre]

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);

[Roberto P]

Thank you for your answer, but isn't (1:end-1) just removing the last value from xbin? Heatmap will still treat those values as center points, so basically I'll have my x axis shifted to the right by half bin lenght.

This is what I get

And this is what I'm looking for

[Cris LaPierre]

Ah, now I see. Unfortunately, heatmaps don't have an XTick setting. You could use the second option I gave you above, which computes the centerpoint of the bin. The only other way I can think to label the edges would be to use histogram2. You'd have to set the edges on both X and Y axes (one extra point in both x and ybin). Also, (0,0) is the bottom left corner.

xbin=[0:0.2:8];
ybin = [1:32];

h = histogram2("XBinEdges",xbin,"YBinEdges",ybin,"BinCounts",flipud(result)');
h.DisplayStyle = 'tile';
h.ShowEmptyBins = 'on';

set(gca,'XTick',xbin,'YTick',ybin);
colormap jet
view(2)
colorbar

[Roberto P]

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]

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]

Yes, they are important. Thank you for the suggestion.

Answer 2

[Walter Roberson]

[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