Logstash: filter to convert string to array of values

[geexee]

Hello,

I have an input log string which contains some easy to regex-matching keywords. I want to index them as an array of values. E.g.

"message"="User's locations: locERTY locRUIE locFGHD locTYUS"

The below code successfully does what I want, in the tag field:

ruby {
    code => 'event.get("message").scan(/loc[A-Z]{4}/).each {|loc| event.tag(loc)}'
}

So, this outputs:

"tags": [
    "locERTY",
    "locRUIE",
    "locFGHD",
    "locTYUS"
]

Now, since I have several such lists, I want to use custom field names, instead of tag. The closest I got was this, which is not perfect because the result output is a key-value pair:

ruby {
    code => 'i=0; event.get("message").scan(/loc[A-Z]{4}/).each {|loc| event.set("[locs][#{i}]",loc); i+=1}'
}

This outputs:

"locs": [
    "0":"locERTY",
    "1":"locRUIE",
    "2":"locFGHD",
    "3":"locTYUS"
]

How can I output a custom loc field similar to the tag one above (with ruby or not)?

Thank you!