10000 [Doc]: add histogram as colorbar example · Issue #30026 · matplotlib/matplotlib · GitHub
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[Doc]: add histogram as colorbar example #30026

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story645 opened this issue May 7, 2025 · 4 comments
Open

[Doc]: add histogram as colorbar example #30026

story645 opened this issue May 7, 2025 · 4 comments
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Documentation: examples files in galleries/examples Documentation topic: color/colorbar

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@story645
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story645 commented May 7, 2025 •
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Problem

Making a colorbar histogram is a kinda popular visualization that's not difficult but I figure finnicky enough that it's worth adding an example to the gallery.

Suggested improvement

I've got one here to explain what I mean but I'm making this an issue so that maybe someone who has a better example can have fun with this:

Image

x = np.random.random(100).reshape(10,10)
counts, bins = np.histogram(x)

cmap = plt.colormaps['viridis']
norm = mcolors.BoundaryNorm(bins, cmap.N)

fig, ax = plt.subplots()
im = ax.imshow(x, cmap=cmap, norm=norm)
cbar = plt.colorbar(im)

cax = ax.inset_axes([1.5, 0, .25, 1])
midpoints = bins[:-1] + np.diff(bins)/2
cax.barh(midpoints, counts, height= 1/len(counts), color = cmap(norm(midpoints)))
cax.set_yticks(bins)
cax.margins(0)
cax.spines[:].set_visible(False)

I'm making cax an inset_axes here mostly because a lot of the real use cases for this are maps where it's nice to have a lot of control on where to put the histogram. I figure this example should live in color. Would be even nicer with #26312 and colorizer 'cause then I think the syncing is managed.
@timhoffm
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timhoffm commented May 8, 2025

I've got one here to explain what I mean but I'm making this an issue so that maybe someone who has a better example can have fun with this:

I suggest you just do this. It's good as is. What could be better?

One maybe could have another dataset. With a more interesting histogram. Try the first one from here. https://matplotlib.org/devdocs/gallery/images_contours_and_fields/image_demo.html

You could leave out the colorbar because the histogram has the same info on the vertical.

Other than that I believe deferring to someone else will likely result in more effort in telling and reviewing without added benefit.

@story645
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story645 commented May 8, 2025

You could leave out the colorbar because the histogram has the same info on the vertical.

Yeah that's mostly there as verification that histogram == colorbar

@timhoffm
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timhoffm commented May 8, 2025

You can also leave it to illustate the point. Then, I'd add a comment on that.

@jklymak
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jklymak commented May 8, 2025

This is a nice idea.

I'd make the bins more purposeful - in the above dataset, bins = np.linspace(0, 1, 11) would be much more useful than the default. Agreed that a better dataset would be more interesting though. Maybe the MRI one would be cool, since it's hard to get a feel for how much of each color there is.

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