How do I order an event study (panel data) dataframe?

Question

I have a big panel database ordered by month and subject with lots of time series variables. In this database several events occure to some of the subjects indicated by a dummy-like variable but with the number of the event.

So I have:

Month	Subject_id	event	Variable_1	Variable_2
01-01-1970	A	0	8%	13%
02-01-1970	A	1	9%	5%
...	...	...	...	...
12-01-1984	B	0	-2%	1%
01-01-1985	B	2	10%	7%
02-01-1985	B	3	26%	3%

I want to construct another database where I can have the months ordered by before-after the event like t-12; t-11; t-10...t; t+1;t+2...

Month	Event	Subject_id	Variable_1	Variable_2
t-1	1	A	8%	13%
t	1	A	9%	5%
...	...	...	...	...
t-1	2	B	-2%	1%
t	2	B	10%	7%
...	...	...	...	...
t-1	3	B	10%	7%
t	3	B	26%	3%

Note that january 1985 is, at the same time, t for event 2 of subject B and t-1 for event 3 of the same subject. For this reason, I couldn't been able to merge by subject and a t+-x column. Some subjects have more than one overlapping event.

How can I transform my data into this new dataframe (I don't care about loosing the subjects that do not have events) ?