Compare values with previous one

To compare cell values with the previous one, you can use the OVER function:

for strings: 
 first([str]) over (previous([rid])) = First([str]) over ([rid]) 

for numbers:
 (first([num]) over (previous([rid])) - First([num]) over ([rid]))=0 

Note: [rid] is a calculated column using rowId() function.

Unfortunately we cannot use rowId() within the over expression as of version 6.5, So we need to create the rid calculated column.