averages of averages for a given day

[S.Peto]

Hi.

I have two columns of data.... column A = dates, column B = money

I have multiple entries for each date. I am trying to return an average of the average of each day for a long list.

I have this:

{=SUMPRODUCT((WEEKDAY($A$2:$A$100,2)=7)*($B$2:$B$100))*(1/COUNTIF(A2:A100,A2:A100))}

It needs to go through the list of dates and when it finds a sunday, add up and average THAT sunday, then find the next sunday and average it, then average the two Sundays together. I need it to work for the future, I add about 500 rows per month..