Pandas- Cumilative Sum Of Previous Row Values

Here is sample dataset: id a 0 5 1 1 5 0 2 5 4 3 5 6 4 5 2 5 5 3 6 9 0 7 9 1 8 9 6 9 9 2 10 9 4 From the dataset, I want to generat

Solution 1:

You can define a functiona like the below:

def cumsum_last3(DF):
    nrow=DF.shape[0]
    DF["sum"]=0
    DF["sum"].iloc[0]=DF["a"].iloc[0]
    DF["sum"].iloc[1]=DF["a"].iloc[0]+DF["a"].iloc[1]
    for a in range(nrow-2):
        cums=np.sum(DF["a"].iloc[a:a+3])
        DF["sum"].iloc[a+2]=cums
    return DF

DF_cums=cumsum_last3(DF)
DF_cums