How to count pairings of cells in spreadsheet

Question

Let's say I have a spreadsheet that has two columns of data. For example:

A    B
1    2
2    3
1    1
1    2
1    3
2    3
2    1 

How could I count the total number of times each pair appears in the spreadsheet. In the example above, 1-2 should have a count of 3 (1 for 2-1, 2 for 1-2), 2-3 should have a count of 2etc

Answer 1

Note that for Excel versions >2007, you can use the new formula COUNTIFS:

[EDIT] Added the correct solution (credits to Chris Nielsen - see the comments)

=COUNTIFS($A$1:$A$12,A1,$B$1:$B$12,B1) + COUNTIFS($A$1:$A$12,B1,$B$1:$B$12,A1)