I'm a little unshore what you're asking for.
It sounds like you want to flatten out two columns into 1:
a b
c d
into
a
b
c
d
If so then may I suggest that awk is your friend here.
It's a full on programming language in a single command.
Code:
awk '{print $1; print $2}'
Its worth looking up some tutorials on awk is so often used for one stage in a pipe when it will do the task of the whole pipe.
If you can't find anything shorter then:
http://www.gnu.org/software/gawk/manual/gawk.html#Regex
For example you often see this in scripts:
grep foo | awk '{print $1}'
Where the developer really ment:
awk '/foo/ {print $1}'