in reply to Simple iteration problem



#!/usr/bin/perl

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The next two lines should be: 

use warnings;
use strict;

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open TAB, "test.txt";

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You should always verify that the file opened correctly: 

open TAB, '<', 'test.txt' or die "Cannot open 'test.txt' $!";

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    $diff = "$tab[0]" - "$seed";

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You are converting the contents of the variables to strings and then subtracting which converts them back to numbers. Just use the variables directly: 

    $diff = $tab[0] - $seed;

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    if ($diff ge 0.1)

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You are using a text comparison operator on numeric data when you should be using a numerical comparison operator: 

    if ($diff >= 0.1)

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{print "@tab\n" && $seed eq $tab[0]}

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The logical AND operator && has relatively low precedence so it is evaluated first and the result of "@tab\n" && $seed eq $tab[0] is passed to the print operator. 

{print "@tab\n"; $seed eq $tab[0]}

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Replies are listed 'Best First'.
Re^2: Simple iteration problem
by toolic (Bishop) on Nov 29, 2007 at 14:53 UTC
    I agree with much of this. However, i think it should be: 
    $seed = $tab[0];

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    Etbr77, here is my version (which is nearly identical to AnonMonk's): 
    use warnings;
use strict;

open TAB, '<', 'test.txt' or die "Can not open file: $!";
my $seed = 1.04;
while (<TAB>) {
    chomp;
    my @tab = split / /;
    my $diff = $tab[0] - $seed;
    if ($diff >= 0.1) {
        print "tab[0]=$tab[0]\n";
        $seed = $tab[0];
    } 
}
close TAB;

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    Since I really have no idea what your input file looks like, I created my own sample input file (test.txt): 
    3
5 6 7
2 22 222
10 9

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    When I run this script, I get the following output: 
    tab[0]=3
tab[0]=5
tab[0]=10

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    If this is not what you are looking for, please provide a small sample of your input, and expected output.

    Update: Removed unnecessary else, thanks to Eimi Metamorphoumai.

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[d/l]
[select]
      I'd just like to add that there's really no reason to include the 
      else {
    next;
};

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      part, since without it the functionality is exactly the same.
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[d/l]
      It works great now! Thank you all very much.
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Re^2: Simple iteration problem
by Anonymous Monk on Nov 29, 2007 at 14:49 UTC
    I used your suggestions to create the following script, which is still not quite right. It spits out all of the values in tab[0], whether or not they meet the criterion of the difference in $seed minus $tab[0] being greater than 0.1 I removed the use warnings and strict, just for the moment. 
    #!/usr/bin/perl


open TAB, '<', 'test.txt' or die "Cannot open 'test.txt' $!";
<TAB>;
$seed = 1.04;
while (<TAB>){
    @tab = split ' ';
    $diff = $tab[0] - $seed;
    if ($diff >= 0.1) {print "@tab\n"; $seed eq $tab[0]} else {next};
}

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[d/l]
      Gah!!

      I removed the use warnings and strict, just for the moment.
      Why, oh why would you do that?

      <tongue_in_cheek>

      Are you trying to make debugging more "interesting" by hiding clues from yourself?

      If so, don't bother reading about "use diagnostics" which may make debugging even less interesting!

      </tongue_in_cheek>

      ...roboticus

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