Going from report to feature matrix
I don't understand what you mean by 


  So I have a report that lists the url and the number of visits a person did. So a combination of ip and url result in an amount of visits.


Assuming that you equate an IP with a user, and you wish to cluster users by their URL visitation frequencies, your matrix, M, would have 


One row per IP (user)
One column for each URL that you are tracking (your features)
and the entries in M would be "visits" of a given URL by a particular IP


Given these assumptions, and your report, M would be:

    abc.be  abc.be/a  abc.be/b
123   5        2         2
321   0        0         4