Address pandas 2.1.0 FutureWarning on wind rose plot

[pablo-benito]

Remove pandas v2.1.0 FutureWarning on Wind Rose plot

Using FLORIS with pandas v2.1.0, the WindRose functions plot_wind_rose triggers a FutureWarning

Example code:

import pandas as pd
from floris.tools.wind_rose import WindRose
import matplotlib.pylab as plt

print(f'Using pandas version {pd.__version__}') 
wr = WindRose()
wr.make_wind_rose_from_user_data([1,2,3], [4,5,6])
wr.plot_wind_rose()

plt.show()

Output:

Using pandas version 2.1.0
Correcting negative Overhang:-2.5
Correcting negative Overhang:-7.5
wind_rose.py:165: FutureWarning: The default of observed=False is deprecated and will be changed to True in a future version of pandas. Pass observed=False to retain current behavior or observed=True to adopt the future default and silence this warning.
  df = df.groupby([c for c in df.columns if c != "freq_val"]).sum()
wind_rose.py:264: FutureWarning: The default of observed=False is deprecated and will be changed to True in a future version of pandas. Pass observed=False to retain current behavior or observed=True to adopt the future default and silence this warning.
  df = df.groupby([c for c in df.columns if c != "freq_val"]).sum()

The default of observed=False in pandas.DataFrame.groupby will change in a future version of pandas, so starting with pandas 2.1.0 it raises a FutureWarning if you don't use it explicitly when grouping by a categorical column. This PR removes those warnings

Related issue

None

Impacted areas of the software

wind_rose.py

Additional supporting information

From pandas v2.1.0 Changelog:

Deprecated the default of observed=False in DataFrame.groupby() and Series.groupby(); this will default to True in a future version (GH 43999)

Test results, if applicable

None

[rafmudaf]

Good catch @pablo-benito, thank you for submitting this update. Also, many thanks for the well described pull request.
Send my hello to the CENER crew 👋