How to do a sliding window in an excel table?

Question

I have a table with a date column and a value column like this

  |A          |B
1 |date       |value
2 |2013-12-10 |1
3 |2013-12-10 |3
4 |2013-12-09 |2
5 |2013-12-04 |5
6 |2013-12-02 |2

Dates can have gaps, duplicates, and don't necessarily need to be sorted.

Now I would like to add a third column, which gives the sum of those values, where the date is within a certain range from the row's date.

E.g. for a range of 6 days, I would expect the following

  |A          |B     |C
1 |date       |value |sum_6
2 |2013-12-10 |1     |6            // 1+3+2
3 |2013-12-10 |3     |6            // 1+3+2
4 |2013-12-09 |2     |7            // 2+5
5 |2013-12-04 |5     |7            // 5+2
6 |2013-12-02 |2     |2            // 2

Can this be done in a formula?

Answer 1

Enter the following into cell C2

=SUMPRODUCT(($A$2:$A$6>=A2-5)*($A$2:$A$6<=A2)*($B$2:$B$6))

then auto-fill downwards, by double-clicking the bottom right corner of cell c2.