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Inconsistent behavior between Normalizers when input is Dataframe #16400

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@alicanb

Description

@alicanb

Bug report

Bug summary
It seems matplotlib.colors.Normalize can work with pandas.Series inputs, whereas LogNorm can't.

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection
from matplotlib.colors import ListedColormap, BoundaryNorm, Normalize, LogNorm
import pandas as pd

x = np.linspace(0, 3 * np.pi, 500)
y = np.sin(x)
dydx = np.linspace(0, 3 * np.pi, 500) +1  # first derivative
df= pd.DataFrame({'x':x,'y':y,'dydx':dydx})
points = np.array([df['x'], df['y']]).T.reshape(-1, 1, 2)
segments = np.concatenate([points[:-1], points[1:]], axis=1)
fig, axs = plt.subplots()

# Create a continuous norm to map from data points to colors
norm = LogNorm(df['dydx'].min(), df['dydx'].max())
lc = LineCollection(segments, cmap='viridis', norm=norm)
# Set the values used for colormapping
lc.set_array(df['dydx'])
lc.set_linewidth(2)
line = axs.add_collection(lc)
fig.colorbar(line, ax=axs)
axs.set_xlim(x.min(), x.max())
axs.set_ylim(-1.1, 1.1)
plt.show()

Actual outcome

TypeError: '<=' not supported between instances of 'SingleBlockManager' and 'int'

Expected outcome

Not sure about what's expected, but if I do Normalize instead of LogNorm it works, if I do lc.set_array(df['dydx'].to_numpy()) instead of lc.set_array(df['dydx']) it also works. It's the combination of LogNorm and pd.Series is the problem.

Matplotlib version

version 3.1.1
module://ipykernel.pylab.backend_inline

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