pandas time series: drop date from index

问题

I have a pandas DataFrame indexed by a DatetimeIndex that holds a time series, i.e. some data as a function of time. Now I would like to plot the behavior over the day regardless of the date. To do so I drop the date:

for date, group in df.groupby(by = df.index.date):
  # drop date
  group.index = group.index.timetz

However, like this I lose a lot of convenience functions of a DatetimeIndex, e.g. it is no longer possible to do things like

df[df.index.hour > 9]

Is there a better way to drop the date?

来源：https://stackoverflow.com/questions/61878736/pandas-time-series-drop-date-from-index