Excel 2007 :: How To Return Previous Sequential Number From A Group

Windows 7, Excel 2007. a formula to find the next lowest sequential number within a group.

Here's an example data set, which represents transactions by date and category:

Col A is a user entered Date which will not be in chronological order (unfortunately a sort is not an option)Col B is a user entered CategoryCol C is a formula that gives the chronological sort order based on the date.

The formula in C2:C9 is =COUNT($A$2:$A$9)-(RANK(A2,$A$2:$A$9)+COUNTIF($A$2:A2,A2)-1)+1Col D is a formula to determine if the row is the first chronological transaction within the Category

The array formula in D2:D9 is =IF(MIN(IF($B$2:$B$9=B2,$C$2:$C$9))=C2,"Y","")

This might not be a necessary column, but can be used as a helperCol E is where I would like a formula to give the next lowest value in Col C for the Category in Col B (the order number in Col C for the previous transaction within the same category).

I have entered in the values that the formula should return in Col E in the table below

A
B
C
D
E

[Code]...

If the current line is the first transaction of the category, the formula should return the value in Col C for that line (so E2 would equal the value in C2, which is 2).

So the first part of the formula could be straightforward, using the helper column:
=IF(D2="Y",C2,

Here's the tricky part: If it's not the first occurrence of the category, then it should return the value of Col C for previous transaction (or the next lowest number in Col C that is within the same category).

E3 would return 4, since the previous transaction for Category A was line 9
C3 = 6, and of all the values of Col C for Category A (2, 4, 6, 8), 4 is the next lowestE4 would return 6, since the previous transaction for Category A was line 3 C4 = 8, and of all the values of Col C for Category A (2, 4, 6, 8), 6 is the next lowestE5 would return 1, since it is the first transaction in Category BE6 would return 1, since the previous transaction for Category B was line 5 C6 = 5, and of all the values of Col C for Catebory B (1, 5, 7), 1 is the next lowestEtc.

I'm thinking I need an array formula to find the minimum value within the category, where that value is less than the value of Col C in the current line. Just not sure how to write that...