Combine multiple columns into one

Hi all,

If there is a loop like following:

Code:

forv y = 2009/2012 {
forv p = 1/20 {
    egen `y'_`p' = mean(var) if year == `y' & portfolio == `p'
}
}

is there a way to combine `y'_`p' into a single column?

Thank you.