With this program code
df['forecast_day'] = pd.to_datetime(df['forecast_day'], format='%Y%m%d')
df['forecast_time'] = pd.to_datetime(df['forecast_time'], format='%H%M')
My current columns of date and time in DataFrame look like this.
forecast_day forecast_time
0 2021-05-05 00:00:00 1900-01-01 12:00:00
1 2021-05-05 00:00:00 1900-01-01 11:00:00
2 2021-05-05 00:00:00 1900-01-01 10:00:00
3 2021-05-05 00:00:00 1900-01-01 09:00:00
4 2021-05-05 00:00:00 1900-01-01 08:00:00
5 2021-05-05 00:00:00 1900-01-01 07:00:00
6 2021-05-05 00:00:00 1900-01-01 06:00:00
7 2021-05-05 00:00:00 1900-01-01 05:00:00
8 2021-05-05 00:00:00 1900-01-01 04:00:00
9 2021-05-05 00:00:00 1900-01-01 03:00:00
10 2021-05-05 00:00:00 1900-01-01 02:00:00
The combined column should look like:
forecast_day&time
0 2021-05-05 12:00:00
1 2021-05-05 11:00:00
2 2021-05-05 10:00:00
3 2021-05-05 09:00:00
4 2021-05-05 08:00:00
5 2021-05-05 07:00:00
6 2021-05-05 06:00:00
7 2021-05-05 05:00:00
8 2021-05-05 04:00:00
9 2021-05-05 03:00:00
10 2021-05-05 02:00:00