Hello friends! i have a google docs excel file that i want to make some changes.

i have some hundreds of lines that consist of 3 rows. They are entries of some expenses and incomes of my company.
an example of a line would be 16/09/2012, Gas, -30 (3 rows which means that at 16/09/12 i spent 30 euros on gas),
another example would be: 17/09/2012, got paid from john, 50 (which means that at 17/09/12 i received 50 euros from john)

What i want to do is create a formula that would automatically create 2 set of lines (of 3 rows again).
one set of rows would be the incomes and the other one would be the expenses (3 rows again).
in order to have the data filtered the formula would probably have to look at the amount of money if it is a negative number or not

THANK you for your time!