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

Hi Monks, I basically have a big file of numbers (over 100 lines) and each line then has numerous numbers again. Obviously the only way to process this is within a loop.
However, my question is, how can I alter my code so that the @good_nums array prints only the values for each particular line, not the accumulated values for the entire file? 


foreach my $line (@file)     {

             #  @array just contains certain values  computed so far  
+          

   for (my $i = 1; $i < @array; $i++)    {


            if ($array[$i - 1] =~ m/(\d+)\s{1}(\d*)/)/   {

                  $x1 = $1;
                  $y1 = $2;
            }


            if ($array[$i] =~ m/(\d+)\s{1}(\d*)/)/   {

                  $x2 = $1;
                  $y2 = $2;
            }


            $equ1 = ($y2 * $y1);
            $equ2 = ($x2 * $x1);

            $equ3 = ($equ1 * $equ2);             
            push @good_nums, $equ3;

   }


 print "@good_nums"; 

}

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Re: value accumulation
by bigj (Monk) on May 15, 2003 at 09:48 UTC
    Sorry, I don't understand really what your input and desired output is. Thus I can't also not follow what your code wants to do. Can you give us an example of your input and a description what good numbers are.
    However, of course, I can rewrite your code to shorten it and make it more Perlish :-) I assume, that the data comes from a file. 
    use Tie::CSV_File;
tie my @array, "Tie::CSV_File", $filename, WHITESPACE_SEPARATED;
for my $i (1 .. $#array) {
    push @good_nums, 
       $array[$i-1]->[0] * $array[$i]->[1] *
       $array[$i-1]->[1] * $array[$i]->[0];
    # Did you really want to compute 4x a multiplication ?!
}
print @good_nums;

    [download]
    Well, I still don't know what's going on :-(
    If the data doesn't come from a file, you could also achieve quite the same, all you have to do is to nest the data: 
    @array = map {[split]} @array;
# instead of the first two lines of my snippet

    [download]

    Greetings,
    Janek

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Re: value accumulation
by Bilbo (Pilgrim) on May 15, 2003 at 11:14 UTC

    Do you just mean that you want to clear @goodnums before processing each line? If so then you probably just want to declare the array within the loop so that it is reinitialised each time 

    foreach my $line (@file) {
    my @good_nums;
    ...
    ...
}

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      When I saw your post I thought "Yes, that's true. But it would be more efficient to declare the @good_nums array outside the look and just empty it". Luckily I did not go ahead and post that, but run a benchmark (In Perl 5.8, ActivePerl build 804, Win2kServer): 

      use Benchmark;
use strict;

sub arrayInit {
    foreach (1..1000) {
        my @list;
        foreach (1..10) {
            push @list, $_;
        }
    }
}

sub arrayUndef {
    my @list;
    foreach (1..1000) {
        foreach (1..10) {
            push @list, $_;
        }
        undef @list;
    }
}

sub arrayEmpty {
    my @list;
    foreach (1..1000) {
        foreach (1..10) {
            push @list, $_;
        }
        @list = ();
    }
}

sub scalarInit {
    foreach (1..1000) {
        my $sum;
        foreach (1..10) {
            $sum += $_;
        }
    }
}

sub scalarUndef {
    my $sum;
    foreach (1..1000) {
        foreach (1..10) {
            $sum += $_;
        }
        undef $sum;
    }
}

sub scalarEmpty {
    my $sum;
    foreach (1..1000) {
        foreach (1..10) {
            $sum += $_;
        }
        $sum = 0;
    }
}

timethese 1000, {
    arrayInit => \&arrayInit,
    arrayUndef => \&arrayUndef,
    arrayEmpty => \&arrayEmpty,
    scalarInit => \&scalarInit,
    scalarUndef => \&scalarUndef,
    scalarEmpty => \&scalarEmpty,
}
__END__

Benchmark: timing 1000 iterations of arrayEmpty, arrayInit, arrayUndef
+, scalarEmpty, scalarInit, sca
larUndef...
arrayEmpty: 15 wallclock secs (13.97 usr +  0.00 sys = 13.97 CPU) @ 71
+.58/s (n=1000)
 arrayInit: 13 wallclock secs (13.45 usr +  0.00 sys = 13.45 CPU) @ 74
+.35/s (n=1000)
arrayUndef: 16 wallclock secs (15.70 usr +  0.00 sys = 15.70 CPU) @ 63
+.68/s (n=1000)
scalarEmpty:  9 wallclock secs ( 9.30 usr +  0.02 sys =  9.32 CPU) @ 1
+07.26/s (n=1000)
scalarInit: 10 wallclock secs ( 9.36 usr +  0.01 sys =  9.37 CPU) @ 10
+6.68/s (n=1000)
scalarUndef: 10 wallclock secs ( 9.43 usr +  0.00 sys =  9.43 CPU) @ 1
+06.01/s (n=1000)

      [download]
      So once again I was wrong :-|

      Thanks for making me try.

      Jenda
      Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.
         -- Rick Osborne

      Edit by castaway: Closed small tag in signature

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