Sorting IP addresses is the canonical example of the Guttman-Rosler Transform (aka the packed default sort) given in A Fresh Look at Efficient Perl Sorting.

The paper is well-worth reading in detail, but here is the IP sorting code.

@out =
  map  substr($_, 4) =>
  sort
  map  pack('C4' =>
    /(\d+)\.(\d+)\.(\d+)\.(\d+)/)
      . $_ => @in;

[download]

Notice that by careful choice of a 'pack' function they can use the default sort behaviour, rather than writing a custom sort routine.

The benchmarks in the paper give this version as being about twice as fast as the Schwartzian Transform.

Update: URL replaced with one that works. Thanks to grinder for pointing it out.

--
<http://www.dave.org.uk>

European Perl Conference - Sept 22/24 2000, ICA, London
<http://www.yapc.org/Europe/>

In reply to RE: Sorting ip addresses quickly by davorg
in thread Sorting ip addresses quickly by DrManhattan

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