Any sane way to filter/remove fields in an array such as [0], [1]?

Hi,

My data contains an array from which I only want to save the message fields. But I don't think you can do regexp on fields in prune, grok or mutate filters (I tried, it didn't work). The problem is that I do not know how many items there will be in the array so I need something like if [myfield][0-9]+[subfields] -> do something.

I know there is the ruby plugin but I don't know ruby.