Re: intermix list of items

[ikegami]

btw, the compare function is suppose to return -1, 0, +1, not just 0 and 1, so I expect your sort has some amount of randomness to it.

Maybe you want something like:

sub intermix { 
   my $a_prime = join('.', reverse(split(/\./, $a)));
   my $b_prime = join('.', reverse(split(/\./, $b)));
   $a_prime cmp $b_prime
}

my @list = ('10.1.1.1', '10.1.1.2', '10.2.2.1', '10.2.2.2');
@list = sort intermix @list;

use Data::Dumper;
print Dumper(@list);

__END__
output
======
$VAR1 = '10.1.1.1';
$VAR2 = '10.2.2.1';
$VAR3 = '10.1.1.2';
$VAR4 = '10.2.2.2';

Almost the same, but more efficient:

sub intermix { 
   my $a_prime = reverse($a);
   my $b_prime = reverse($b);
   $a_prime cmp $b_prime
}

my @list = ('10.1.1.1', '10.1.1.2', '10.2.2.1', '10.2.2.2');
@list = sort intermix @list;

use Data::Dumper;
print Dumper(@list);

__END__
output
======
$VAR1 = '10.1.1.1';
$VAR2 = '10.2.2.1';
$VAR3 = '10.1.1.2';
$VAR4 = '10.2.2.2';

This is the same thing as the last, but probably more efficient, especially for longer lists:

my @list = ('10.1.1.1', '10.1.1.2', '10.2.2.1', '10.2.2.2');
@list = map { $_->[0] } 
        sort { $a->[1] cmp $b->[1] }
        map { [ $_, ''.reverse($_) ] } 
        @list;

use Data::Dumper;
print Dumper(@list);

__END__
output
======
$VAR1 = '10.1.1.1';
$VAR2 = '10.2.2.1';
$VAR3 = '10.1.1.2';
$VAR4 = '10.2.2.2';

Note: Given addresses of the form 'a.b.c.d', the above snippets only work well if there is there is a common 'd' of for every 'a.b.c' in the list.

[ikegami]

Here's an algorithm that doesn't suffer from the problem mentioned in the Note above:

my @list = ('10.1.1.[1..2]', '10.2.2.[1..2]', '10.3.3.[3..6]');

my @list_prime = 
   map {
      my $n = $_;
      $n =~ s/\[(\d+)\.\.(\d+)\]//;
      [ $n, $1, $2 ]
   } @list;

my @ordered_list;

my $done;
do {
   $done = 1;
   foreach (@list_prime) {
      next unless defined($_);
      if ($_->[1] > $_->[2]) { undef($_); next }
      push(@ordered_list, $_->[0].($_->[1]++));
      $done = 0;
   }
} while (!$done);


use Data::Dumper;
print Dumper(@ordered_list);

__END__
output
======
$VAR1 = '10.1.1.1';  # First  from first.
$VAR2 = '10.2.2.1';  # First  from second.
$VAR3 = '10.3.3.3';  # First  from third.
$VAR4 = '10.1.1.2';  # Second from first.
$VAR5 = '10.2.2.2';  # Second from second.
$VAR6 = '10.3.3.4';  # Second from third.
$VAR7 = '10.3.3.5';  # Third  from third.
$VAR8 = '10.3.3.6';  # Fourth from third.

It can probably be optimised.