While issues

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

I'm sure fresher eyes will come up with a better solution - or just tell me what's wrong with this

my $cnr = 0;
while ($cnr < 1) {
    my $xda = int rand (0 .. $total);
    if ( $aob[$xda][ $y - 1 ] ne q{}) {
        $aob[$x][$y] = $z + $aob[$xda][ $y - 1 ];
        $cnr++;
    }
}
[download]

What this is supposed to do is find the first non-empty randomly chosen member of @aob line $y-1 (which has numbers and blanks) and assign that value plus $z to $aob[$x][$y]. Unfortunately,the script just sits with a blinking cursor at this section, so I assume it's in a loop.

Warnings and strict are on, no warnings.

Now, I do have a cludgy work around

Never mind - looking back at my cludgy work around and tweaking it:

my @delarray = ( 0 .. $total )
my $cnr = 0;
my @dlarray  = shuffle @delarray;
for my $xd ( 0 .. $total ) {
    my $xda = $dlarray[$xd];
    if ( $cnr <= 1 && defined $aob[$xda][ $y - 1 ] ) {
        $aob[$x][$y] = $z + $aob[$xda][ $y - 1 ];
        $cnr++;
   }
}
[download]

Comment on While issues Select or Download Code

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Re: While issues by ikegami (Patriarch) on Feb 03, 2011 at 15:58 UTC
`rand(0 .. $total)` [download] should be `rand($total+1)` [download] Actually, it probably be should be `rand(0+@aob)` [download] If any element of `@aob` can be picked, why rely on some external value. (Technically, the "0+" is unnecessary because of rand's prototype, but that's fairly obscure.) By the way, `$cnr` is unneeded. I also got rid of q{} because it just doesn't stand out as much as the default quotes. `while (1) { my $xda = int rand( 0+@aob ); if ( $aob[$xda][ $y - 1 ] ne "") { $aob[$x][$y] = $z + $aob[$xda][ $y - 1 ]; last; } }` [download]	[reply] [d/l] [select]
Re: While issues by wind (Priest) on Feb 03, 2011 at 15:54 UTC
Your problem is here: `my $xda = int rand (0 .. $total);` [download] rand only takes a single parameter, so you're selecting a random number from 0 to 0 currently. This is probably what you intended: `my $xda = int rand $total;` [download] -Miller	[reply] [d/l] [select]
Re^2: While issues by ikegami (Patriarch) on Feb 03, 2011 at 16:01 UTC
Off by one. That will never return `$total`. `rand` returns a value that's "up to but not including" its argument.	[reply] [d/l] [select]
Re: While issues by kennethk (Abbot) on Feb 03, 2011 at 15:55 UTC
There is nothing fundamentally wrong with the while portion of the construct. My guess would be that your conditional `$aob[$xda][ $y - 1 ] ne q{}` never evaluates to true. Are you sure it contains what you think it does? See How can I visualize my complex data structure? (short answer Data::Dumper). On a side note, if `$cnr` is never used outside this context, I would use last (see Loop Control) to control flow: `while (1) { my $xda = int rand (0 .. $total); if ( $aob[$xda][ $y - 1 ] ne q{}) { $aob[$x][$y] = $z + $aob[$xda][ $y - 1 ]; last; } }` [download] Update: I think ~~wind~~ikegami has the answer ~~above~~below.	[reply] [d/l] [select]
Re: While issues by ikegami (Patriarch) on Feb 03, 2011 at 16:08 UTC
The code in your update is functionally different than your original code. Did you mean to go from finding one non-empty element to two? (original: `$cnr < 1` vs new: `$cnr <= 1`). Also, it loops more than necessary. The following fixes this and simplifies the code: `my $cnr = 2; for my $xda ( shuffle 0 .. $total ) { if ( defined $aob[$xda][ $y - 1 ] ) { $aob[$x][$y] = $z + $aob[$xda][ $y - 1 ]; last if --$cnr == 0; } }` [download] Or if you mean to only find one non-empty element: `for my $xda ( shuffle 0 .. $total ) { if ( defined $aob[$xda][ $y - 1 ] ) { $aob[$x][$y] = $z + $aob[$xda][ $y - 1 ]; last; } }` [download]	[reply] [d/l] [select]
Re^2: While issues by Dandello (Monk) on Feb 03, 2011 at 16:36 UTC
Your initial solution was SO much better than mine. So that's the one I'm using. I needed to find the first random non-blank element. Using shuffle worked, but I was looking for a neater and simpler way. Again, thank you. My final - `while (1) { my $xda = int rand $total + 1; if ( defined $aob[$xda][ $y - 1 ] ) { $aob[$x][$y] = $z + $aob[$xda][ $y - 1 ]; last; } }` [download] . Using 'defined' is actually better in this case than using "" or q{}. No warnings.	[reply] [d/l]
Re: While issues by Dandello (Monk) on Feb 03, 2011 at 16:07 UTC
So many good solutions, and so much better than my cludge I knew it was something dumb and simple - I rarely bollux up the complicated ones, but simple... And ikegami's solution worked like a charm. Thank you	[reply]