How to loop through array in Logstash?

Hello,

I have this data:

"url" => [
      [0] [
          [0] "",
           [1] "data",
            [2] "data1"
[3] "9462"
        ],

What I want is that I need to get last element of list as assignment_1 ( I need to assing last data into this variable) and the other things need to placed in assignment_2 as "data/data1".
I though it would be useful if have used loop over array list but could not figured it out.
Think that my array lenght will be changed all the time.But again, I need last data into assignmet_1 and the other into assingment_2.

I would do that in ruby. Start off with

ruby {
    code => '
        url = event.get("url")
        if url
            event.set("a1", url[0][-1])
            event.set("a2", url[0][0..-2].join("/"))
        end
    '
}

Thank you so much. It works really good. Especially, I was suffering to code

this part.
This might be a another question but when I split a field logstash deletes its value instead of keeping it. I want to split a field but dont want to loose its value. How am I gonna do that?

You need to show an example of the event input, the filter configuration, and the resulting event.