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Add an "extend" keyword to colors.BoundaryNorm #4850

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fmaussion opened this issue Aug 1, 2015 · 4 comments
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Add an "extend" keyword to colors.BoundaryNorm #4850

fmaussion opened this issue Aug 1, 2015 · 4 comments
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v3.3.0

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@fmaussion
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I've always found the third colorbar example from the gallery quite inelegant (http://matplotlib.org/examples/api/colorbar_only.html). Very often, you would like to extend your colorbar while using the same color scheme as the current colormap, not by adding new colors with set_over and set_under.

Maybe I am missing something, but the current behaviour without set_over leads to the same color for the last box of the colorbar and the extension. I found it quite easy to add a new extend keyword to the existing BoundaryNorm class that does the exact same thing as before but handles the color choice differently. It is best shown with the example below:

import matplotlib as mpl
from matplotlib import pyplot
fig = pyplot.figure(figsize=(8,3))
ax1 = fig.add_axes([0.05, 0.80, 0.9, 0.15])
ax2 = fig.add_axes([0.05, 0.475, 0.9, 0.15])
ax3 = fig.add_axes([0.05, 0.15, 0.9, 0.15])
bounds = [-1, 2, 5, 7, 12, 15]
cmap = mpl.cm.get_cmap('jet')

# Default behavior
norm = mpl.colors.BoundaryNorm(bounds, cmap.N)
cb1 = mpl.colorbar.ColorbarBase(ax1, cmap=cmap,
                                     norm=norm,
                                     extend='both',
                                     orientation='horizontal')
cb1.set_label('Default BoundaryNorm ouput');

# With the new keyword
norm = mpl.colors.BoundaryNorm(bounds, cmap.N, extend='both')
cb2 = mpl.colorbar.ColorbarBase(ax2, cmap=cmap,
                                     norm=norm,
                                     # Ideally this keyword could 
                                     # be omitted since it is redundant
                                     extend='both',
                                     orientation='horizontal')
cb2.set_label('With the new keyword');

# Just max
norm = mpl.colors.BoundaryNorm(bounds, cmap.N, extend='max')
cb3 = mpl.colorbar.ColorbarBase(ax3, cmap=cmap,
                                     norm=norm,
                                     extend='max',
                                     orientation='horizontal')
cb3.set_label('Just max');

Which produces:
colorbar_demo

What do you think? If accepted I could easily add it to my ongoing PR
@fmaussion fmaussion mentioned this issue Aug 1, 2015
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@efiring
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efiring commented Aug 1, 2015

It should be a separate PR. I see the logic of what you want, but we need to be careful about how this relates to other uses of "extend" (colorbar and contourf) and to other norms.

@fmaussion
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Sounds reasonable: I'll wait for the current PR to be closed first.

@fmaussion fmaussion mentioned this issue Sep 7, 2015
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@fmaussion
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The new related PR: #5034

@tacaswell tacaswell mentioned this issue Sep 13, 2015
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@JosjaVanBever JosjaVanBever mentioned this issue Feb 22, 2022
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@rcomer
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rcomer commented Dec 10, 2022

Looks like this was done at #17534.

@rcomer rcomer closed this as completed Dec 10, 2022
@QuLogic QuLogic added this to the v3.3.0 milestone Dec 13, 2022
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@efiring @QuLogic @fmaussion @rcomer