如何将 datetime.time() 对象转换为 datetime.datetime 对象 pandas

Question

import pandas as pd
import datetime
df = pd.DataFrame([{'st':datetime.datetime.strptime('21:00:00','%H:%M:%S').time(),'et':datetime.datetime.strptime('22:00:00','%H:%M:%S').time()}, {'st':datetime.datetime.strptime('1:00:00','%H:%M:%S').time(),'et':datetime.datetime.strptime('3:00:00','%H:%M:%S').time()}])


Out[183]: df
         et        st
0  22:00:00  21:00:00
1  03:00:00  01:00:00

I would like to be able to convert the above dataframe with new fields having datetime.datetime objects with two other extra columns such as here having any dummy date in it and using the time from their respective rows:

      et        st      sdate_time                edate_time
0  22:00:00  21:00:00   2018-01-01 21:00:00      2018-01-01 22:00:00  
1  03:00:00  01:00:00   2018-01-01 1:00:00       2018-01-01 3:00:00

The approach I have tried is using apply method

df['et'].apply(lambda et: pd.datetime.combine(datetime.datetime.strptime('2018-01-01', '%Y-%m-%d').date(),et))

but turns out that the dataframe could be really huge and I would like to vectorize the above operation without the apply method .

Answer 1

Try this

date = str(datetime.datetime.strptime('2018-01-01', '%Y-%m-%d').date())

df['edate_time'] = pd.to_datetime(date + " " + df.et.astype(str))

       et          st            edate_time
0   22:00:00    21:00:00    2018-01-01 22:00:00
1   03:00:00    01:00:00    2018-01-01 03:00:00

Answer 2

Try:

df.assign(sdate_time=pd.to_datetime(df['et'], format='%H:%M:%S'), 
          edate_time=pd.to_datetime(df['st'], format='%H:%M:%S'))

Output:

         et        st          sdate_time          edate_time
0  22:00:00  21:00:00 1900-01-01 22:00:00 1900-01-01 21:00:00
1  03:00:00  01:00:00 1900-01-01 03:00:00 1900-01-01 01:00:00

Answer 3

Is there no better way of doing this than to assign a random date?

I have matplotlib version '3.3.1' and still face this issue of not being able to plot a datetime.time object for which I do not need a date but only the 24 hours of a day.

I've seen workarounds for the label, using import matplotlib.dates as mdates but still not the best way.