Pandas groupby: percentage above threshold

Question

I have a DataFrame that I\'m looking to use a groupby on but I\'m looking for a little bit of an unusual function to aggregate with. I would like to get the per

Answer 1

>>> df.groupby('day')['value'].apply(lambda c: (c>0).sum()/len(c))
day
1      0.333333
2      0.666667
3      0.333333
4      1.000000
Name: value, dtype: float64