How do I access to a value for event and event-1

Hi,

I need to display value (string) of a field depending on the value of this field in previous event. Something like this :

if previous_event.field = "toto" then display current_event.field else display "anomaly" I've found something interesting with "transatcion" by I can't achieve to do this.

Any help is welcome.

Thanks in advance.

Regards