Plotting vertical line on matplotlib stacked area graph-CodePudding

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.

CodePudding user response：

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)