using parameter expansion sorting flags

[Rory Mulvaney <rorymulv@xxxxxxxxx>]

Hello,

I have a few filenames that I put into an array with:

PNMFILES=( f.*.{Atop,Bbot}.pnm )

the ordered contents of this array become:

f.0009.Atop.pnm f.0010.Atop.pnm f.0011.Atop.pnm f.0012.Atop.pnm
f.0009.Bbot.pnm f.0010.Bbot.pnm f.0011.Bbot.pnm

Now I can't figure out how to order them in an array, using the parameter
expansion sorting flags n and o, as:

f.0009.Atop.pnm f.0009.Bbot.pnm f.0010.Atop.pnm f.0010.Bbot.pnm
f.0011.Atop.pnm f.0011.Bbot.pnm f.0012.Atop.pnm

Also I'd like the resulting resorted array PNMFILES2 to be such that:

echo ${PNMFILES2[2]} 

yields:

f.0009.Bbot.pnm

rather than some single character.

Thanks and regards again,
Rory