Kapacitor processing streaming data with a specific columns

Hello folks.

is it possible to have kapacitor working on a specific column and outputs only the column it worked on as result?

Basically I have a feed contains few columns

tag1, tag2, col1, col2, col3

I only need few metrics of, say, col2. So i came up with something like

`var my_stream = stream

var first_value = my_stream|first(‘col2’).as(‘value’)
var last_value = my_stream|last(‘col2’).as(‘value’)

.as(‘first’, ‘last’)
However, this does not work because the result will simply contains all columns of the original stream. Plus, it will rename all columns like first.xxx, second.xxxx.