mata
mata drop varmatch()
real vector function varmatch(from, to)
{
	matches = J(1,rows(to),0)
	for (i=1; i<=rows(from); i++) {
		matchi = (from[i,2]:==to[.,2])'
		matches = matches + matchi
	}
	return(matches)
}

//varmatch(A2c, A4c)'
//select(A4c, varmatch(A2c,A4c)')
//select(A4c, 1:-varmatch(A2c,A4c)')
end

mata
mata drop varmatchpos()
real vector function varmatchpos(from, to)
{
	matches = J(1,rows(from),0)
	for (i=1; i<=rows(to); i++) {
		matchi = (from[.,2]:==to[i,2])':*i
		matches = matches + matchi
	}
	return(matches)
}
//S2 = J(1,cols(A4),.)
//S2[1,varmatchpos(A2c, A4c)] = A2
//S2
//S3[1,varmatchpos(A3c, A4c)] = A3
//S1[1,varmatchpos(A1c, A4c)] = A1
//S3
//S1

end