Comparison result capture???

shemp has asked for the wisdom of the Perl Monks concerning the following question:

Hi all, i was working on a function to sort ip like strings, and ran into a couple of odd things. Well, here is the sort function - it could be done differently i know, but it shows my situation:

use strict;
...
sub ip_sorter {
[download]

my $a_parts = split /\./, $a; my $b_parts = split /\./, $b;

    my @a_parts = split /\./, $a;
    my @b_parts = split /\./, $b;

    my $result;
    map { return $result if $result = ($a_parts[$_] <=> $b_parts[$_]) 
+} (0 .. $#a_parts);
[download]

so, 1 issue i had was that i couldnt put "no strict" in the map block. I dont know why this is, any insight would be great.

Also, i was unable to find any variable that perl implicitly sets as the result of a comparison. Im thinking something analogous to $! - the value of C errno. So lets just pretend that $^C gets set to the result of the last comparison operation. then i could rewrite my sort with this line:

...
   map { return $^C if ($a_parts[$_] <=> $b_parts[$_]) };
...
[download]

I've looked for this variable at search.cpan.org/author/JHI/perl-5.8.0/pod/perlvar.pod to no avail.

Fixed typo at author's req - dvergin 2003-05-14

Comment on Comparison result capture??? Select or Download Code

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Re: Comparison result capture??? by pzbagel (Chaplain) on May 14, 2003 at 17:20 UTC
I know that you are looking at this from another perspective but if you are indeed sorting IPs, converting them to a numerical equivalent from dotted decimal and then sorting them numerically is a slick way to go. I didn't write it, but here is a post from dws on IP sorting. It uses pack to convert the IPs and then a sweet Orcish Maneuver to speed up the sort. HTH	[reply]
Re: Comparison result capture??? by chip (Curate) on May 14, 2003 at 16:22 UTC
You're assigning the split results to scalars but not using those scalars in the map block, which seems a bit, well, odd. What's up with that? As for the "last result" idea, `foreach` (which is spelled "`for`" by all good monks) will often serve the purpose of avoiding duplicate expressions: `$_ and return $_ for $a_parts[$_] <=> $b_parts[$_];` I've also run into odd restrictions on `no strict` and I really wish I understood what was broken by accident and what on purpose WRT that. Finally, I'll take off a fractional style point for using a `map` block where you really meant `foreach`.... -- Chip Salzenberg, Free-Floating Agent of Chaos	[reply] [d/l] [select]
Re: Comparison result capture??? by boo_radley (Parson) on May 14, 2003 at 17:10 UTC
speaking of odd, your use of `for` for a 1 element array is pretty novel all in its own right.	[reply]
Re: Re: Comparison result capture??? by chip (Curate) on May 14, 2003 at 20:41 UTC
I wish I could say I'd invented that, but I stole it from Tom C. I don't know whether he stole it in turn.... -- Chip Salzenberg, Free-Floating Agent of Chaos	[reply]
Re: Re: Comparison result capture??? by dragonchild (Archbishop) on May 14, 2003 at 16:58 UTC
Didn't you mean `my $x; ($x = $a_parts[$_] <=> $b_parts[$_]) && return $x for 0 .. $#a_parts;` [download] You're using $_ too many times. ------ We are the carpenters and bricklayers of the Information Age. Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement. Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.	[reply] [d/l]
Re: Re: Re: Comparison result capture??? by chip (Curate) on May 14, 2003 at 20:44 UTC
I'll grant you that my code uses $_ with more than one meaning, and some people may not like that. But it's clear enough to me. Seems to work, too. -- Chip Salzenberg, Free-Floating Agent of Chaos	[reply]
Re: Re: Comparison result capture??? by shemp (Deacon) on May 14, 2003 at 18:00 UTC
Oops! I meant to split $a and $b into @a_parts and @b_parts, which makes a lot more sense. I have submitted a change request to the editors.	[reply]
Re: Comparison result capture??? by flounder99 (Friar) on May 14, 2003 at 19:57 UTC
You can always sort IPs like this `use strict; my @ips = ( "1.2.3.4", "1.2.3.5", "1.2.3.3", "2.2.3.4", "1.0.2.3"); @ips = map {$_->[1]} sort {$a->[0] cmp $b->[0]} map { [ join(".", map {sprintf "%03d", $_} split('\.', $_) ), $_ ] } @ips; print join "\n", @ips; __OUTPUT__ 1.0.2.3 1.2.3.3 1.2.3.4 1.2.3.5 2.2.3.4` [download] -- flounder	[reply] [d/l]


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