Create reference to sorted anonymous array

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

Hi Monks,

my Google-Fu so far didn't produce any results for my question so I'm trying to obtain the answer here. :)
To keep it simple I creates a small test script. I'm creating a new array and give a reference of it to a function which simply prints the array elements.
Now I want to do the same for a reverse sorted array (basially reverse @array) without having to save the reverse output into a second array but so far I'm struggling to do that.

use strict;
use warnings;
sub blubb($)
{
        my $array_ref = shift;
        for(my $i = 0; $i <= $#$array_ref; ++$i)
        {
                print "$i $array_ref->[$i]\n";
        }
}
my @array = (1, 2, 3);
blubb(\@array);
[download]

Now I could simply do:

my @array2 = reverse @array;
blubb(\@array2);
[download]

My question is: Is there a way to do this without @array2 ?
Can I use blubb() directly with the reverse sorted @array ?

So far I haven't been able to come up with the syntax for this. :(

Thanks a lot in advance.

Comment on Create reference to sorted anonymous array Select or Download Code

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Re: Create reference to sorted anonymous array by choroba (Cardinal) on Mar 16, 2016 at 14:32 UTC
Use square brackets to create an anonymous array: `blubb([reverse @array]);` [download] Also, remove the `($)` prototype. See Far More than Everything You've Ever Wanted to Know about Prototypes in Perl -- by Tom Christiansen to know why. ($q=q:Sq=~/;[c](.)(.)/;chr(-\|\|-\|5+lengthSq)`"S\|oS2"`map{chr \|+ord }map{substrSq`S_+\|`\|}3E\|-\|`7**2-3:)=~y+S\|`+$1,++print+eval$q,q,a, [download]	[reply] [d/l] [select]
Re^2: Create reference to sorted anonymous array by Digioso (Sexton) on Mar 16, 2016 at 14:54 UTC
Thanks a lot. It's working with that. :) I'll also check out the link you posted.	[reply]
Re: Create reference to sorted anonymous array by Marshall (Canon) on Mar 17, 2016 at 00:48 UTC
Another suggestion for you in addition to that from choroba . C style for() loops are actually quite rare in Perl. They are prone to the dreaded and most common programming error, the "off by one error". Here is another way to write blubb(). `use strict; use warnings; sub blubb { my $array_ref = shift; my $i =0; foreach (@$array_ref) #dereferences the ref to an array { print $i++, " $_\n"; } } my @array = (1, 2, 3); blubb([reverse @array]); __END__ Prints: 0 3 1 2 2 1` [download]	[reply] [d/l]
Re^2: Create reference to sorted anonymous array by Digioso (Sexton) on Mar 17, 2016 at 13:42 UTC
Thanks for the tip. :) For me the C-Syntax has stuck somehow. The C-Loop provides a more readable syntax in my opinion and I'm trying to avoid using $_ as much as possible because someone else besides me might have to read my code. And when I learned programming my teachers told me to use variable names that state what they're used for. Although my school days are long gone I'm still sticking to that. OK, in my example @array and sub blubb are no such names obviously. :P Even this works btw: `foreach (@$array_ref) { print; }` [download]	[reply] [d/l]
Re^3: Create reference to sorted anonymous array by choroba (Cardinal) on Mar 17, 2016 at 17:01 UTC
If all you need is names, add them: `for my $element (@array) { print $element, "\n"; }` [download] And, for completeness, iterating over indices: `for my $index (0 .. $#array) { print "$index: $array[$index]\n"; }` [download] ($q=q:Sq=~/;[c](.)(.)/;chr(-\|\|-\|5+lengthSq)`"S\|oS2"`map{chr \|+ord }map{substrSq`S_+\|`\|}3E\|-\|`7**2-3:)=~y+S\|`+$1,++print+eval$q,q,a, [download]	[reply] [d/l] [select]
Re^3: Create reference to sorted anonymous array by AnomalousMonk (Archbishop) on Mar 17, 2016 at 18:45 UTC
Further to choroba's reply: For even more complete completeness, if you're dealing with array references: `for my $element (@$arrayref) { print $element, "\n"; } for my $i (0 .. $#$arrayref) { print "$i: $arrayref->[$i]\n"; }` [download] Update: Digioso: I quite agree with your preference for using explicitly named variables rather than default names (or none at all) in the interests of readability and maintainability. I disagree that the C-style `for`-loop serves these interests, quite apart from the lurking demon Offbyone. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^4: Create reference to sorted anonymous array by Digioso (Sexton) on Mar 18, 2016 at 09:40 UTC
Re^5: Create reference to sorted anonymous array by AnomalousMonk (Archbishop) on Mar 18, 2016 at 12:08 UTC
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Re^3: Create reference to sorted anonymous array by Marshall (Canon) on Mar 18, 2016 at 21:40 UTC
As choroba and others have mentioned, I actually seldom use $_ and give an actual name to the var. This doesn't slow the code down a bit and makes it more readable. `foreach my $line (@$array_ref) { print $line; }` [download] is just fine !! I write and lot of C code (and also ASM). I can tell you that the very, very most common error in programming is the "off by one" error. The `foreach()` syntax avoids that possibility. There are a lot of programs out there that sometimes break in mysterious ways due to memory allocation errors and other issues related to the "off by one" problem. the foreach() syntax avoids this problem. You early instruction will serve you well. There is just a different way to do it in Perl than in C.	[reply] [d/l] [select]