Average if in Python with 2 time series

Question

I want to average the mean value like the average if function in python.

For example let's say I have a set of ranks for A,B,C,D as 'df' like this picture:

and I want the average of the dollar amounts according to the 'ranks':

For example, I want the average dollar amount of top two ranks (1 and 2)

I've tried to get boolean dataframes first

top = ranks < 3
bot = ranks >=3 

and tried to loop through it but i don't know if this is the correct way to approach this. thanks alot for your help!

Answer 1

ranks = pandas.DataFrame([[1,2,3,4], [1,3,2,4]], columns=['A','B', 'C', 'D'], index=['2000-01-31', '2000-02-01'])
amounts = pandas.DataFrame([[1,4,1,1], [1,1,1,1]], columns=['A','B', 'C', 'D'], index=['2000-01-31', '2000-02-01'])

top = amounts[ranks<3].mean(axis=1)
bot = amounts[ranks>=3].mean(axis=1)
amounts['top mean'] = top
amounts['bot mean'] = bot

ranks

            A  B  C  D
2000-01-31  1  2  3  4
2000-02-01  1  3  2  4

amounts

            A  B  C  D  top mean  bot mean
2000-01-31  1  4  1  1       2.5       1.0
2000-02-01  1  1  1  1       1.0       1.0