时间序列数据提取

Question

I have data set in format given bellow. I am interested to extract data points every after 3H.

   Unnamed: 0                Date  ...  a_anox1  a_anox2
0           0 2017-11-01 00:00:41  ...   3.6465      0.0
1           1 2017-11-01 00:01:41  ...   3.9795      0.0
2           2 2017-11-01 00:02:41  ...   4.2055      0.0
3           3 2017-11-01 00:03:41  ...   4.4490      0.0
4           4 2017-11-01 00:04:41  ...   4.6375      0.0

[5 rows x 12 columns]

I want to extract data points every after 3H the outputs:

   Unnamed: 0                Date  
0           0 2017-11-01 00:00:41  
1           1 2017-11-01 03:00:41 
2           2 2017-11-01 06:00:41  
3           3 2017-11-01 09:00:41  
4           4 2017-11-01 12:00:41  

[5 rows x 12 columns]

Answer 1

Use resample . Set your datetime column to index df.set_index('date_column', inplace=True) and then use resample :

import pandas as pd

# data with hours differe 
df = pd.DataFrame({'symbol':range(13)}, index=pd.date_range(start='01-12-2020', freq='H', periods=13))   

# example data get 3rd hour last value
last3h = df.resample('3H').last()   

print(last3h)

See resample in Pandas documentation for more details and use cases.