my @cols;
for my $row (@array) {
    my @f = split /,/, $row;
    $f[2] = $b[$f[2]];
    push @{$cols[$_]}, $f[$_] for 0 .. $#f;
}

##</code><code>##

my %col_for = (
    foo => 2,
    bar => 4,
    baz => 5,
);

my @cols;
for my $row (@array) {
    my @f = split /,/, $row;
    splice @f, $col_for{$f[1]} || 6, 0, shift @b;
    push @{$cols[$_]}, $f[$_] for 0 .. $#f;
}