'Group by month and divide the average of one column by the average of the other?

I have two columns A and B. I want to divide the mean of A by the mean of B.

df['Test']= df.groupby('Month').apply(lambda x: df['A'].mean().astype(float)/df['B'].mean().astype(float))

Help me, where is the error?

Solution 1:^[1]

DATA['C'] = DATA.apply(lambda x: np.array([x.A, x.B]), axis=1)

pandas requires all rows to be of the same length so the problem of uneven pandas series shouldn't be present

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Solution	Source
Solution 1	w_sz