How to add previous output values as input values in python dataframe

Question

I have 3 dataFrames a,b, and c.I want to calculate the sum of a+b+previous output(c).

a=pd.DataFrame([1,2,3,4])
b=pd.DataFrame([1,2,3,4])
c=pd.DataFrame([])
c=c.append(a+b+c.shift(1))

Here I have already to dataframes a and b ,then i created a new dataframe c for saving output of the calculation."c.shift(1) means the previous output.

It shows error.How it is possible??

It would be helpful if you could give an example of what output you expect. — divingTobi
– divingTobi, Commented Sep 8, 2020 at 9:12

Gil Pinsky · Accepted Answer · 2020-09-08 09:14:23Z

2

Appending will only work in a loop and will not return a value so you could do it but your computation can be reduced to cumsum in this case:

a=pd.DataFrame([1,2,3,4])
b=pd.DataFrame([1,2,3,4])
c=(a+b).cumsum()

answered Sep 8, 2020 at 9:14

Gil Pinsky

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