Using pandas to group rows and find average

Question

I have a data frame like this

   amount
0   351
1   684
2   931
3   186
4   412
5   674

I want to add a new column called like 3 days average which contains values equal to the average of the amount of current row and 2 rows above it. For example the 3davg of row 2 = (931+684+351)/3, row 3 = (186+931+684)/3. Final result should be looking like this

   amount   3davg
0   351      DNE
1   684      DNE
2   931      655
3   186      600
4   412      509
5   674      424

I have to achieve it in a big data frame and will be having flexible ~davgs, how would I do it in pandas?

Answer 1

df['3davg'] = df.rolling(window=3).mean()