Drop complete row or message

Elastic Stack Logstash
1

Hi,
I want to drop full row based on one of the field. I am using following in filter.

filter {
        grok {
            match => {"message" => ["%{IP:ip} %{SPACE}\{user:%{USERNAME:UserId}\}"]}
        }
        date {
            locale => "en"
            timezone => "UTC"
            match => ["timestamp", "dd/MMM/yyyy:HH:mm:ss"]
            target => "@timestamp"
        }

        if "ANONYMOUS" in [UserId] {
            drop { }
        }
        else {
           }
        }

When I run, this, all log lines end up in kibana only difference is that all fields like ip and userID are -.

Also I want to process all log files in folder created after specific time. is there any filter for that?

2

Only difference between what and what?