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[Bug]: barplot does not show anything when x or bottom start and end with NaN #23687

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Gullumluvl opened this issue Aug 20, 2022 · 4 comments · Fixed by #23751
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[Bug]: barplot does not show anything when x or bottom start and end with NaN #23687

Gullumluvl opened this issue Aug 20, 2022 · 4 comments · Fixed by #23751
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status: confirmed bug
Milestone
v3.6.1

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@Gullumluvl
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Bug summary

I am not sure if this is a bug or an optimization, but in most cases it is fine to plot bars of arrays containing NaN (only the NaN values are not displayed, the rest is ok).

Here I found that when the x array or the bottom array have NaNs at the extremities, no bar is displayed.

(barh has the same behavior).

Code for reproduction

import numpy as np, matplotlib as mpl, matplotlib.pyplot as plt

barx = np.arange(3, dtype=float)
barheights = np.array([0.5, 1.5, 2.0])
barstarts=np.array([0.77]*3)

barx[[0,2]] = np.NaN
# alternatively:
#barstarts[[0,2]] = np.NaN

fig, ax = plt.subplots()

ax.bar(barx, barheights, bottom=barstarts)
# Not ok, nothing shown!

# Same behavior with ax.barh:
ax.barh(barx, barheights, left=barstarts)

# However, the behavior is correct when NaN only affect the 'heights' argument:

fig, ax = plt.subplots()
ax.bar(np.arange(3), np.array([np.NaN, 1, np.NaN]), bottom=np.array([0.2, 0.3, 0.4]))
# OK, one bar is displayed.

Actual outcome

zero bar displayed

Expected outcome

Non-NaN elements should be shown

Additional information

No response

Operating system

Ubuntu 20.04.3

Matplotlib Version

3.5.3

Matplotlib Backend

TkAgg, pdf

Python version

3.8.10

Jupyter version

ipython

Installation

pip
@tacaswell tacaswell added this to the v3.7.0 milestone Aug 26, 2022
@tacaswell
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I can reproduce this, but do not understand it yet.

@tacaswell
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In 7c4b000 / #12903 we added some logic to make sure that width would work with interesting units, notable time deltas and and datetime data.

To do this we effective add the width to the first element of the x data, run it through the conversion machinery, and then subtract off the already converted value of the first data point to convert the "width" in (possibly unitful) user data into our internal version of it. However, if the first point in nan, then the width is poisoned to also be nan which means that when we make the Rectangles the x positions are nan which then (correctly) does not render anything.

@jklymak
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jklymak commented Aug 26, 2022

I guess we should be using the new safe_first_element excluding NaNs?

@tacaswell
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The new one only drops None, but I just finished adapting it to work with nan as well. PR shortly....

tacaswell added a commit to tacaswell/matplotlib that referenced this issue Aug 26, 2022
@tacaswell
FIX: show bars when the first location is nan
cfb27b3 
Due to the way we handle units on the bar width having an invalid value in the
first position of the x bar (of y of barh) would effectively poison all of the
widths making all of the bars invisible.

This also renames the cbook function _safe_first_non_none function ->
_safe_first_finite and adjusts the behavior to also drop nans

closes matplotlib#23687
@tacaswell tacaswell mentioned this issue Aug 26, 2022
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2 tasks
@QuLogic QuLogic modified the milestones: v3.7.0, v3.6.1 Sep 19, 2022
melissawm pushed a commit to melissawm/matplotlib that referenced this issue Dec 19, 2022
@tacaswell @melissawm
FIX: show bars when the first location is nan
4e79d8d 
Due to the way we handle units on the bar width having an invalid value in the
first position of the x bar (of y of barh) would effectively poison all of the
widths making all of the bars invisible.

This also renames the cbook function _safe_first_non_none function ->
_safe_first_finite and adjusts the behavior to also drop nans

closes matplotlib#23687
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FIX: show bars when the first location is nan tacaswell/matplotlib
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@tacaswell @QuLogic @jklymak @Gullumluvl