opposite of df.diff() in pandas

Question

I have searched the forums in search of a cleaner way to create a new column in a dataframe that is the sum of the row with the previous row- the opposite of the .diff() function which takes the difference.

this is how I'm currently solving the problem

df = pd.DataFrame ({'c':['dd','ee','ff', 'gg', 'hh'], 'd':[1,2,3,4,5]}
df['e']= df['d'].shift(-1)
df['f'] = df['d'] + df['e']

Your ideas are appreciated.

Answer 1

You can use rolling with a window size of 2 and sum:

df['f'] = df['d'].rolling(2).sum().shift(-1)

    c  d    f
0  dd  1  3.0
1  ee  2  5.0
2  ff  3  7.0
3  gg  4  9.0
4  hh  5  NaN