[FIXED] Plotting vertical line on matplotlib stacked area graph

Issue

I trying to plot a stacked area graph using matplotlib with vertical line(s) on top. My MWE is:

  import numpy as np
  import pandas as pd
  import matplotlib.pyplot as plt

  # my data
  df = pd.DataFrame(data={'date': pd.date_range(start='2020-09-01', freq='D', periods=100),
                          'x1': np.random.randint(80,200,size=100),
                          'x2': np.random.randint(50,90,size=100),
                          'x3': np.random.randint(50,100,size=100),
                         })
  df = df.set_index('date')

  df0 = df.query("index == 20201026")  # points of interest

  fig = plt.figure()
  ax = fig.add_subplot(111)
  df.plot(ax=ax, kind='area')
  ax.vlines(df0.index, ymin=0, ymax=1000, color='k', lw=1)
  # ax.vlines(pd.concat([df0,df0], axis=0).index, ymin=0, ymax=1000, color='k', lw=1, ls='--')
  ax.set_ylim((0,400))
  ax.legend(loc='lower right')
  plt.show()

The area graph is plotted using df and any point(s) of interest are in df0. If there is just one point in df0, when I plot using vlines I get an error

TypeError: ufunc 'isfinite' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

But if I use pd.concat([df0,df0], axis=0), there's no problem with vlines. Why does this happen? I can't find anything in the docs that say vlines must accept more than one vertical line.

Solution

Matplotlib doesn't know how to deal with pd.Index. Use tolist to solve the problem:

ax.vlines(df0.index.tolist(), ymin=0, ymax=1000, color='k', lw=1)
#             HERE ---^

Solution proposed by @BigBen:

#                        HERE ---v
df.plot(ax=ax, kind='area', x_compat=True)
ax.vlines(df0.index, ymin=0, ymax=1000, color='k', lw=1)

Answered By - Corralien