Splitting value from one row to other rows in the same column in pandas

Question

I have a question regarding to pandas

I have got a DataFrame df

TaskId	UserId	Hours
123456	123456	19
123456	123456	NaN
123456	123456	NaN
123456	123456	NaN
654321	654321	10

Now I want to split the 19 from the first row into equal amounts where the TaskId and UserId is the same 19 / 4 = 4.75

This is what I would like to receive

TaskId	UserId	Hours
123456	123456	4.75
123456	123456	4.75
123456	123456	4.75
123456	123456	4.75
...	...	...

I couldn't find anything here on stackoverflow

thank you

Answer 1

Use GroupBy.transform for divide first values by counts:

g = df.groupby(['TaskId','UserId'])['Hours']
df['Hours'] = g.transform('first').div(g.transform('size'))
print (df)

   TaskId  UserId  Hours
0  123456  123456   4.75
1  123456  123456   4.75
2  123456  123456   4.75
3  123456  123456   4.75
4  654321  654321  10.00