[Omaha.pm] Sort quickie

[Jay Hannah]

On Jul 7, 2004, at 3:07 PM, Miller, Scott L (Omaha Networks) wrote:
> Another interesting possibility, expanding on what Jay started;
> it might be possible to use Jay's technique to sort IP addresses
> without first converting the addresses to their "long int" form...

cmp was driving me crazy so I jumped on IRC (irc.freenode.net #perl)...

The 2nd code block below is an IPv4 IP sorter for you... The 1st code 
block is a faulty one. -grin-

j


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This content is stored as  http://sial.org/pbot/3335.

From: "Omaha" at 68.13.20.113
Summary: Confused by cmp

I was writing a quick demo of how to sort IPv4 addresses. The problem 
is that the by_ip sort below should NOT work, as I undestand cmp, yet 
somehow it already does...

Shouldn't "sort @x" and "sort by_ip @x" as written below both return 
the same series? I thought '$a cmp $b' was the default behavior of 
sort?

Confused...

my @ips = qw(
    20.0.50.0
    20.0.100.0
    77.0.0.0
    100.0.0.0
);

print join ", ", sort @ips;
print "\n";
print join ", ", sort by_ip @ips;
print "\n";

sub by_ip {
    my ($a, $b) = @_;
    $a cmp $b;
}

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<pasteling> "Omaha" at 68.13.20.113 pasted "Confused by cmp" (23 lines, 
554B) at http://sial.org/pbot/3335
<broquaint> Omaha: that's because you're comparing two undef vars i.e 
$a & $b aren't put in @_, they're magical package level vars
<broquaint> drop my($a,$b) = @_ and it works as expected
<Omaha> ... ahhh... ok. So my cmp always returned 0, leaving the array 
in original order, which just happened to be sorted by IP already. Got 
it...
<Omaha> Any way to local($a, $b) so I can manipulate them? -ponder- 
Just trying to save a couple lines of code I guess...
<apeiron> Maybe more descriptive variable names would be a prudent idea.
* Omaha grins
<broquaint> avoid $a & $b outside of sort { ... }, it saves all sorts 
of headaches

-----------

This content is stored as  http://sial.org/pbot/3336.

From: "Omaha" at 68.13.20.113
Summary: sort by_ip -- feedback anyone?

Quick and dirty IPv4 sorter?

my @ips = qw( 20.0.100.0 20.0.50.0 100.0.0.0 77.0.0.0 );

print join ", ", sort @ips;
print "\n";
print join ", ", sort by_ip @ips;
print "\n";

sub by_ip {
    my ($j, $k) = ($a, $b);
    for ($j, $k) {
       $_ = sprintf("%03d.%03d.%03d.%03d", split /\./);
    }
    $j cmp $k;
}

------------------------

<pasteling> "Omaha" at 68.13.20.113 pasted "sort by_ip -- feedback 
anyone?" (17 lines, 327B) at http://sial.org/pbot/3336
<cfedde> Omaha: I'd use Sockets, inet_aton and {$a cmp $b}
<cfedde> Omaha: but yours works too

---------------

<apeiron> Beware False Hubris (inventing your own wheel), False 
Impatience (thinking you can make one more quickly than it'd take to 
learn an existing one), and False Laziness (thinking that making your 
own is less effort).

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<nictuku> is this fine? if (!$lasttimestamp) { $lasttimestamp = 0; }
<Omaha> $lasttimestamp ||= 0;
<nictuku> Omaha, cool.
<Omaha> ya. :)