Pandas rolling mean in dataframe

import pandas as pd
import numpy as np

Create a dataframe

df = pd.DataFrame({'B': range(5)})

df.index = [pd.Timestamp('20190101 09:00:00'),
pd.Timestamp('20190101 09:00:02'),
pd.Timestamp('20190101 09:00:03'),
pd.Timestamp('20190101 09:00:05'),
pd.Timestamp('20190101 09:00:06')]

df

	B
2019-01-01 09:00:00	0
2019-01-01 09:00:02	1
2019-01-01 09:00:03	2
2019-01-01 09:00:05	3
2019-01-01 09:00:06	4

Create a rolling dataframe mean by time interval

#here it will create a rolling mean of the previous two records in the dataframe
#e.g. (0, (0+1)/2, (1+2)/2, etc)
df.rolling(2, min_periods=1).mean()

	B
2019-01-01 09:00:00	0.0
2019-01-01 09:00:02	0.5
2019-01-01 09:00:03	1.5
2019-01-01 09:00:05	2.5
2019-01-01 09:00:06	3.5