Python Forum

I have a file, df, that I wish to take the delta of every 7 day period and reflect the timestamp for that particular period

df:

Date Value
10/15/2020 75
10/14/2020 70
10/13/2020 65
10/12/2020 60
10/11/2020 55
10/10/2020 50
10/9/2020 45
10/8/2020 40
10/7/2020 35
10/6/2020 30
10/5/2020 25
10/4/2020 20
10/3/2020 15
10/2/2020 10
10/1/2020 5


**Desired Output:**






Date Value

10/9/2020 30
10/2/2020 30




10/15/2020 to 10/9/2020 is 7 days with the delta being: 75 - 45 = 30
10/9/2020 timestamp would be: 30 and so on




This is what I am doing:


for row in df.itertuples():
callDate = datetime.strptime(row.Date, "%m/%d/%y %I:%M %p")
previousRecord = df['Date'].shift(-6).strptime(row.Date, "%m/%d/%y %I:%M %p")
Delta = Date - previousRecord



I am thinking I may be able to do this as well:


df=df.assign(Delta=df.Sun.sub(df.Monday),Date=pd.Series\ (pd.date_range(pd.Timestamp('2020-01-01'), periods=7, freq='7d')))[
[['Delta','Date']]

Any suggestion is appreciated

Since rows corresponds days you can just shift the data frame on 6 positions and compute difference between shifted and original ones:

(df.shift(6).iloc[:, 1] - df.iloc[:,1])[df.index % 6 == 0].dropna()