Bfill on Groupby object
df.sort_values(by = 'rank', inplace = True)
df = df.assign(Values1 = lambda x: x['rank'] == 1).fillna(method = 'bfill')
df.groupby(by = 'Group')['Values']
I have a table that looks like this




index
Group
rank
Values




0
a
2
344.0


1
a
3
NaN


2
b
1
455.0


3
a
1
NaN


4
b
2
NaN




I want to group data by 'Group', then sort according to 'rank' and then bfill only for rank == 1. The dataset is very big so I want to avoid loops.
I tried
temp[temp['rank']<=2].sort_values('rank', ascending = True).groupby('Group').bfill(axis='rows', inplace = True)
but this gives me
"backfill() got an unexpected keyword argument 'axis'"