Comparing entity against previous entity in views Say my view lists people and their salaries using data from their profile..

Abby, 10000, O
Amelie, 10000, O
Alan, 15000, O
Ben, 15000, O
Bertie, 20000, O
Boris, 20000, O
Carl, 20000, O
Carol, 25000, O
Derek, 25000, O


How can I change the third column to an X when the salary changes?

Abby, 10000, X
Amelie, 10000, O
Alan, 15000, X
Ben, 15000, O
Bertie, 20000, X
Boris, 20000, O
Carl, 20000, O
Carol, 25000, X
Derek, 25000, O


I'm guessing I do it in hook_views_pre_render($view), but there are so many variables/objects in the $view, I don't know where to start.

I don't think it matters, but I'm using views_data_export to output this into a CSV.
Probably late by now, but have you tried using revisions? You can pull in individual fields that has any revision.