Comparing lists from day1 with the list of day2 and etc. to get difference

[igschloessl]

I need to compare a list consisting of one field from day1 to day2 and get what values where not listed on day 1 but in day2
Comparing this with day 3 and so on.

so for example I have a list with user agents and I want to detect what user agents I have today comparing to the last days. Or comparing one week with another week.

Can I do this automated?

Thank you in advance