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raise informative error message on misshapen input to set_offsets #22408

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raise informative error message on misshapen input to set_offsets #22408

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@ianhi ianhi commented Feb 5, 2022

PR Summary

Fixes: #22401

Importantly allows this:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()

scat = ax.scatter([0,.5], [0, .5])
scat.set_offsets([[],[]])
plt.show()

PR Checklist

Tests and Styling

  • Has pytest style unit tests (and pytest passes).
  • Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

  • [NA] New features are documented, with examples if plot related.
  • [NA] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
  • [NA] API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
  • [NA] Documentation is sphinx and numpydoc compliant (the docs should build without error).

ianhi
ianhi commented Feb 7, 2022
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lib/matplotlib/tests/test_collections.py Outdated
modified = mcollections.Collection(
offsets=np.column_stack([[0, 1], [0, 1]])
)
modified.set_offsets([[], []])
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@ianhi ianhi Feb 7, 2022

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I think that this should actually be column_stack and I should get rid of the transpose in the set method. Most usage will be with column_stack i suspect.

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@timhoffm timhoffm Feb 9, 2022

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Please check what other set_offsets methods do. We should aim for consistency.

@matplotlib matplotlib deleted a comment from ianhi Feb 10, 2022
@matplotlib matplotlib deleted a comment from ianhi Feb 10, 2022
@tacaswell tacaswell added this to the v3.6.0 milestone Mar 29, 2022
tacaswell
tacaswell requested changes Mar 29, 2022
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lib/matplotlib/collections.py Outdated
(np.asarray(self.convert_xunits(offsets[:, 0]), 'float'),
np.asarray(self.convert_yunits(offsets[:, 1]), 'float')))

if offsets.shape == (2, 0):
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@tacaswell tacaswell Mar 29, 2022

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Suggested change
if offsets.shape == (2, 0):
if offsets.shape == (0, 2):

Which will require some changes to the tests.

The docs say(N, 2) so this should be the degenerate case of ((N, 2), .., (2, 2), (1, 2), (0, 2)) (the (2,) case is a special case for spelling (1, 2)).

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@ianhi ianhi Dec 12, 2025 •
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I think (0,2) just works fine in the else block? This branch is necessary to handle the special case of offsets=[[],[]]

import numpy as np
np.asanyarray([[],[]]).shape
# (2, 0)

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@ianhi ianhi Dec 12, 2025

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ah wait I think I understand better. You're saying that [[],[]] is not really a valid input? becuase that's like saying I have two points each with zero data, which doesn't make any sense I guess.

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tacaswell commented Mar 29, 2022

Anyone can dismiss my review

@jklymak jklymak marked this pull request as draft March 30, 2022 10:52
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jklymak commented Mar 30, 2022

Fell free to move out of draft...

@tacaswell tacaswell modified the milestones: v3.6.0, v3.7.0 Aug 19, 2022
@QuLogic QuLogic modified the milestones: v3.7.0, v3.8.0 Jan 7, 2023
@ksunden ksunden modified the milestones: v3.8.0, future releases Aug 8, 2023
@tacaswell tacaswell mentioned this pull request Apr 15, 2024
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tacaswell commented Apr 15, 2024

Looking at this again, I think my comment is still valid.

@ianhi ianhi changed the title allow setting collection offsets to empty raise informative error message on misshapen input to set_offsets Dec 12, 2025
@ianhi ianhi marked this pull request as ready for review December 12, 2025 19:03
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ianhi commented Dec 12, 2025 •
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Looking again myself I now understand and agree with @tacaswell 's comment. and have updated this PR to instead throw the error message that would have set me on the right track.

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@timhoffm timhoffm timhoffm approved these changes

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status: needs revision topic: collections and mappables

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[Bug]: PolyCollection set_offsets does not accept [[], []] like Line2D

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@ianhi @tacaswell @jklymak @timhoffm @QuLogic @ksunden