How do I create a function that adds up certain numbers in one column that
all have a certain value in another column. For example:
column A Column B
557 4
557 6
445 7
336 20

The values are offset by different numbers of rows as well. Ideally I'd want
to know the sum of all of Column B whose Column A value is the same. There
are about a 1000 of unique values in Column A so I don't want to have to go
and do this by hand.

Thanks.