Analyzing Paypal Spreadsheet. Finding First Instance of a Buyer

Hi...

I've been trying to apply various tutorials to solve my particular problem to no avail... i suppose mine would be a very common issue but i see no postings about a solution..

ok so...

i have the last 8 months of paypal records. I want to

a. mark the very first occurance of every email address for one time buyers and repeat buyers chronologically. So... i will know how many new customers we served every day.

b. total up the gross payment amounts of each new customer after any date. For instance, if we did a seminar in april, I want to know the total spending of only the new customers ... defined as anyone who has not purchased anything from january to the date of the seminar.


help??? =)