my @foo = qw/C1 C12 R5 C3 C21 C2 D12/;
@foo =
  map { $_->[0] . $_->[1] }
  sort { $a->[0] cmp $b->[0] or $a->[1] <=> $b->[1] }
  map { [/(\D*)(\d*)/] } @foo;
print join( ", ", @foo ) . "\n";