How to fill in rows with repeating data in pandas?

Question

In R, when adding new data of unequal length to a data frame, the values repeat to fill the data frame:

df <- data.frame(first=c(1,2,3,4,5,6))
df$second &         


        

Answer 1

In my case I needed to repeat the values without knowing the length of the sub-list, i.e. checking the length of every group. This was my solution:

import numpy as np
import pandas 

df = pandas.DataFrame(['a','a','a','b','b','b','b'], columns=['first'])

list = df.groupby('first').apply(lambda x: range(len(x))).tolist()
loop = [val for sublist in list for val in sublist]
df['second']=loop

df
  first  second
0     a       0
1     a       1
2     a       2
3     b       0
4     b       1
5     b       2
6     b       3