in reply to Yet more While issues

For clarity more than for speed, 

my $offset = splice @cPosns, rand @cPosns, 1;

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should be 
my $offset = $cPosns[rand @cPosns];

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and 
while (1) {
   ...
   last;
}

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should simply be 
...

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For speed, don't copy the zazb argument into a local variable. Access $_[3] directly.

A possible tweak: 

push @cPosns, pos $zazb while $zazb =~ m{(?=c)}g;

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might be faster as 

push @cPosns, $-[0] while $zazb =~ m{c}g;

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or maybe even 

my $pos = -1;
push @cPosns, $pos while ($pos = index($zazb, 'c', $pos+1)) >= 0;

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Benchmark and find out.

Which I just can't seem to get my head around to get it to work without throwing 'undefined value' warnings all over the place.

This will occur when 'c' doesn't occur in $zazb. Based on your first snippet, you want 

sub popnum3 {
    my ( $x, $y, $z ) = @_;  # $_[3] is $zazb
    if ( $y == 0 ) {
        $aob[$x][0] = $initial * ( 1 + $z );
    }
    else {
        my @cPosns;
        push @cPosns, $-[0] while $_[3] =~ m{c}g;
        if (@cPosns) {
            my $offset = $cPosns[rand @cPosns];
            $aob[$x][$y] = $aob[$offset][ $y - 1 ] * ( 1 + $z );
        }
    }
    return $aob[$x][$y];
}

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Replies are listed 'Best First'.
Re^2: Yet more While issues
by Dandello (Monk) on Mar 16, 2011 at 22:04 UTC

    I got it - at least it's stopped throwing warnings and it's a whole lot faster that what I had before.

    Since popnum3 is called from inside an if/else 

    else {
   my $pos = -1;
   push @cPosns, $pos while ($pos = index($zazb, 'c', $pos+1)) >= 0;
   my $offset = $cPosns[rand @cPosns];
   $cell = sprintf '%.2f', popnum3( $x, $y, $copycop, $offset, );
}

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    then 
    sub popnum3 {
    my ( $x, $y, $z, $offset ) = @_;
    if ( $y == 0 ) {
        $aob[$x][0] = $initial * ( 1 + $z );
    }
    else {
        while (1) {
            $aob[$x][$y] = $aob[$offset][ $y - 1 ] * ( 1 + $z );
            last;
        }
    }
    return $aob[$x][$y];
}

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    So far it's looking good. Thanks

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      What's with the useless while(1) { ...; last; } again?
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        Habit

        I'm still trying to get everything configured to work right - When I have the code set up like this: 

        else {
   my $pos = -1;
   push @cPosns, $pos while ($pos = index($zazb, 'c', $pos+1)) >= 0;
   my $offset = $cPosns[rand @cPosns];
   $cell = sprintf '%.2f', popnum3( $x, $y, $copycop, $offset, );
}

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        then 
        sub popnum3 {
    my ( $x, $y, $z, $offset ) = @_;
    if ( $y == 0 ) {
        $aob[$x][0] = $initial * ( 1 + $z );
    }
    else {
        while (1) {
            $aob[$x][$y] = $aob[$offset][ $y - 1 ] * ( 1 + $z );
            last;
        }
    }
    return $aob[$x][$y];
}

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        It's reiterating over the entire string for every single 'a' or 'c' which starts fast then slows to a crawl

        When I move this section 

         my $pos = -1;
   push @cPosns, $pos while ($pos = index($zazb, 'c', $pos+1)) >= 0;

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        above all the if/else's, to just under where $zazb is defined, then the $offset variable in 
        else {
   my $offset = $cPosns[rand @cPosns];
   $cell = sprintf '%.2f', popnum3( $x, $y, $copycop, $offset, );
}

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        becomes undefined when imported into popnum3.

        So obviously I'm still missing something.

        There is always at least 1 'c' in the string so that's not the problem.

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[d/l]
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Re^2: Yet more While issues
by Dandello (Monk) on Mar 18, 2011 at 05:20 UTC

    Back to square one I guess. This 

     sub popnum3 {
    my ( $x, $y, $z ) = @_;  # $_[3] is $zazb
    if ( $y == 0 ) {
        $aob[$x][0] = $initial * ( 1 + $z );
    }
    else {
        my @cPosns;
        push @cPosns, $-[0] while $_[3] =~ m{c}g;
        if (@cPosns) {
            my $offset = $cPosns[rand @cPosns];
            $aob[$x][$y] = $aob[$offset][ $y - 1 ] * ( 1 + $z );
        }
    }
    return $aob[$x][$y];
}

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    only seems to work relatively short strings, but not when the string gets much more than 500 characters. Then it throws 'uninitialized value in $offset' errors which I'm guessing means the algorithm didn't find the one 'c' that had to be there.

    I admit I'm at my wit's end here. This looks like it should work, but it doesn't. There is a 'c' in every row, so that's not the problem.

    THIS works 

    sub popnum3 {
    my ( $x, $y, $z, $zazb ) = @_;
    if ( $y == 0 ) {
        $aob[$x][0] = $initial * ( 1 + $z );
    }
    else {
        while (1) {
            my $xda = int rand( $total + 1 );
            
            if ( substr( $zazb, $xda, 1 ) eq 'c' ) {
                $aob[$x][$y] = $aob[$xda][ $y - 1 ] * ( 1 + $z );
                last;
            }
        }
    }
    return $aob[$x][$y];
}

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    But takes about 5 seconds per row on the full array and since there's 8400 rows in the full run, that's about 12 hours.

    Getting the run time down would be very helpful.

    Thanks

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[d/l]
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      Then it throws 'uninitialized value in $offset' errors

      I don't believe you when you say that snippet produced that warning.

      Then it throws 'uninitialized value in $offset' errors which I'm guessing means the algorithm didn't find the one 'c' that had to be there.

      No. If it doesn't find any 'c', it never uses $offset.

      PS - Don't count out half the warning (not even counting the line number).

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