How to find business date of last year

June 29, 2022

I’m trying to find last year business date based on df last row but I have a problem that my datatable just has data on business date. So if last year date was weekend, nothing shows.

Below is my sample code:

import pandas as pd
import numpy as np
from datetime import datetime as dt
from pandas.tseries.offsets import BDay

df = pd.DataFrame({'Date':['20210625','20220626'],'Amount':[10,20]})
df['Date'] = pd.to_datetime(df['Date'],infer_datetime_format=True)
date_1 = df['Date'].iloc[-1]
date_2 = date_1 - pd.DateOffset(years=1)
df_2 = df[df['Date'] == date_2]
df_2

So what I need is that how to find date_2 as the recent business date of the same date of last year. For example in this case is 2021-06-25.

Thank you.

>Solution :

The question is a bit unclear, I’ll answer the How to find the "recent business date of the same date of last year" part:

from pandas.tseries.offsets import BDay

df['lastYear'] = df['Date']-pd.DateOffset(years=1)+0*BDay()

output:

        Date  Amount   lastYear
0 2021-06-25      10 2020-06-25
1 2022-06-26      20 2021-06-28

previous BDay if not a BDay:

from pandas.tseries.offsets import BDay

df['lastYear'] = df['Date']-BDay(1)-pd.DateOffset(years=1)+BDay(1)

output (with more examples):

        Date  Amount   lastYear
0 2021-06-25      10 2020-06-25
1 2022-06-24      20 2021-06-24
2 2022-06-25      30 2021-06-25
3 2022-06-26      40 2021-06-25
4 2022-06-27      50 2021-06-25
5 2022-06-28      60 2021-06-28