Is there a way to add a new field to all the documents in a index in kibana ? For example , lets assume, i have the age of all the users in my elastic kibana. And i want to separate them into two categories as Below 50 and Above 50 . So if there is a user who is 23 years of age , he should have a category value as Below 50.
I'd like to add another option to the one offered by @dravit. If you don't want to modify your documents, and you only need that extra field to run analysis in Kibana, you can add a scripted field to your index pattern, so that the category value is calculated at query time.
Ref: https://www.elastic.co/guide/en/kibana/current/scripted-fields.html
The script for your scripted field would be something as easy as
doc['age'].value > 50 ? "Above 50" : "Below 50"