Exporting one field of matrix/table to text file

I’m looking for a way to export the list of rsids (and only the rsids, not the whole row) from my matrix to a text file, one id per row, but can’t seem to find a way.

I converted the rows to a table, but short of exporting the whole table, I couldn’t find a way either.
Using table.to_pandas() and then keeping only the column(s) of interest is slow, surely there’s a better option that escapes me?


the key_by() is needed because select will keep key fields, so we need to un-key the table first.

That makes sense, both the key.by() and the select() (I tried mt.rsid.export() but of course that couldn’t work).
Thank you.