Pandas: Adding An Excel Sumif Column Like =a1/sumif(b:b,b1,a:a)

I have a pandas DataFrame like: pet treats lbs 0 cat 2 5.0 1 dog 1 9.9 2 snek 3 1.1 3 cat 6 4.5 4 dog 1 9.4 I would like to add a fourt

Solution 1:

You can using transform

df['treat_rate']=df.treats/df.groupby('pet').treats.transform('sum')
df
Out[153]: 
    pet  treats  lbs  treat_rate
0   cat       2  5.0        0.25
1   dog       1  9.9        0.50
2  snek       3  1.1        1.00
3   cat       6  4.5        0.75
4   dog       1  9.4        0.50