You may want to consider dumping the logs into a database and manipulating the data there. Then you can export what you need back into a CSV file. This would give you much more flexibility if your requirements change later on.

Look at MySql, SQLite or others. The DBI/DBD modules can interface a large number of databases. Of course this would mean learning some SQL, but the basics are not difficult.

You may also want to look at DBD::CSV which appears to let you treat CSV files as a database, and manipulate them using SQL statements through DBI (disclaimer: I have not tried this module myself).