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BoundaryNorm yield a ZeroDivisionError: division by zero #17579

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ghost opened this issue Jun 5, 2020 · 3 comments · Fixed by #17830
Closed

BoundaryNorm yield a ZeroDivisionError: division by zero #17579

ghost opened this issue Jun 5, 2020 · 3 comments · Fixed by #17830
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Difficulty: Easy https://matplotlib.org/devdocs/devel/contribute.html#good-first-issues status: confirmed bug
Milestone
v3.4.0

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@ghost
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ghost commented Jun 5, 2020

Bug report

Bug summary

import matplotlib as mpl
import matplotlib.pyplot as plt
cmap = plt.cm.jet
bounds = [0, 1]
norm = mpl.colors.BoundaryNorm(bounds, cmap.N)
norm(0.5)

Gives:

---------------------------------------------------------------------------
ZeroDivisionError                         Traceback (most recent call last)
<ipython-input-160-8a8135eaeb3c> in <module>
      2 bounds = [0, 1]
      3 norm = mpl.colors.BoundaryNorm(bounds, cmap.N)
----> 4 norm(0.5)

/usr/local/lib/python3.6/dist-packages/matplotlib/colors.py in __call__(self, value, clip)
   1442             iret[xx >= b] = i
   1443         if self._interp:
-> 1444             scalefac = (self.Ncmap - 1) / (self.N - 2)
   1445             iret = (iret * scalefac).astype(np.int16)
   1446         iret[xx < self.vmin] = -1

ZeroDivisionError: division by zero

Expected outcome

not an error: just an integer.

Matplotlib version

mpl.__version__: 3.2.1
os.name: posix
mpl.get_backend(): module://ipykernel.pylab.backend_inline
sys.version: 3.6.9 (default, Apr 18 2020, 01:56:04) 
[GCC 8.4.0]
$ jupyter --version
jupyter core     : 4.6.3
jupyter-notebook : 6.0.3
qtconsole        : 4.7.1
ipython          : 7.13.0
ipykernel        : 5.1.1
jupyter client   : 6.0.0
jupyter lab      : 1.2.14
nbconvert        : 5.6.1
ipywidgets       : 7.5.1
nbformat         : 4.4.0
traitlets        : 4.3.3
@tacaswell tacaswell modified the milestones: v3.3.0, v3.4.0 Jun 5, 2020
@tacaswell tacaswell added the Difficulty: Easy https://matplotlib.org/devdocs/devel/contribute.html#good-first-issues label Jun 5, 2020
@tacaswell tacaswell modified the milestones: v3.4.0, v3.3.0 Jun 5, 2020
@tacaswell
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This code path was changed a bin on master branchhttps://github.com//pull/17534 but does not fix this issue.

We need to add logic to

matplotlib/lib/matplotlib/colors.py

Lines 1488 to 1490 in af7beaa

if self.Ncmap > self._N:
scalefac = (self.Ncmap - 1) / (self._N - 1)
iret = (iret * scalefac).astype(np.int16)
to handle the case were we only have 1 bin.

Sorry for the milestone thrashing.

@dstansby dstansby mentioned this issue Jul 3, 2020
Merged
@Raghibshams456
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is anybody is doing or done something on this issue .?...

@tacaswell
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Yes, this should be fixed by #17830 (which is still under review) and if it is merged will be available in mpl 3.4 (which we are aiming for a Sept release).

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Difficulty: Easy https://matplotlib.org/devdocs/devel/contribute.html#good-first-issues status: confirmed bug
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Milestone
v3.4.0
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Fix BoundaryNorm for multiple colors and one region dstansby/matplotlib
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@tacaswell @Raghibshams456