Re^4: column counter and printf question

Hi Bill,

Thanks for the reply and the link, I get it now. Although one more question, should (@columns-3) maybe be ($columns-3)?

Also, I'm a bit confused over the fact that the following pieces of code produce different output files. Can you take a look at the scripts and let me know where the problem is, as I can't understand it?

 #/bin/perl/

use strict;
use warnings;

open my $input, '<', './2kc29-out.txt'  or die $!;
open my $output, '>', 'test_thu1.txt' or die $!;

while (my $line = <$input>) {

  chomp $line;            
  $line =~ s/^\s+//;      

  next if 1 .. $line =~ /\@TYPE xy/; #perlop range operators

  my @columns = split(/\s+/, $line);
  my $format = "%8.3f" . "%10.3f"x(@columns-3) . "\n";
  printf $output $format, @columns[2..$#columns];                     
  
}
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and the second one:

 #/bin/perl/

use strict;
use warnings;

open my $input, '<', './2kc29-out.txt'  or die $!;
open my $output, '>', 'test_thu2.txt' or die $!;

while (my $line = <$input>) {

  chomp $line;            
  $line =~ s/^\s+//;      

  next if 1 .. $line =~ /\@TYPE xy/; #perlop range operators

  my @columns = split /\s+/, $line;  

  my $col1 = shift@columns;  # column 1 (ignore)
  my $col2 = shift@columns;  # column 2 (ignore)
  my $col3 = shift@columns;  # column 3 (keep) 

  my $result = printf $output ("%8.3f",$col3); # column 3 format

  # loop over remaining columns
  for my $c (@columns) {
    my $data = printf $output ("%10.3f",$c);
    $result .= " $data";  # append $result
 }
    printf $output "$result\n";                    
}
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The second script, prints a slightly bigger file (37.51MB over 31,28MB) because in the output it has printed dozens of random "1" numbers right after the last column. Why is this happening?

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Re^5: column counter and printf question
by Athanasius (Archbishop) on Oct 29, 2015 at 12:53 UTC

should (@columns-3) maybe be ($columns-3)?

No, there is no variable named $columns. In scalar context, @columns is the same as scalar @columns, which returns the number of elements in the @columns array. Since you want 3 less than the total number of array elements, @columns - 3 is correct.

Can you take a look at the scripts and let me know where the problem is, as I can't understand it?

The problem is with these lines in the second script:

my $result = printf ...
...
my $data = printf ...
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In both cases, printf should be sprintf. The latter returns the formatted string, which is what you want; the former returns “true” on success, hence the 1 numbers in the second output file. As the code now stands in the second script, the line my $data = printf $output ("%10.3f",$c); prints the formatted output to the output file, and sets $data to 1; then at the end of the for loop, all those 1s are printed to the file. You need something like this (untested):

my $result = sprintf("%8.3f", $col3); # column 3 format

# loop over remaining columns
for my $c (@columns) {
    my $data = sprintf("%10.3f", $c);
    $result .= " $data";  # append $result
}

print $output "$result\n";
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Note that with this logic you don’t print to the output file until after the loop finishes.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^6: column counter and printf question

by fasoli (Beadle) on Oct 29, 2015 at 14:45 UTC

Yes, that makes sense now. I actually counted the "1s" and they are 78 - as many as my columns, so now I see how printf also returned "true". Indeed, sprintf does the trick. Thanks for the explanation, I would have never thought that the problem was with printf.

Now I know 2-3 different ways to count columns, the difference between printf and sprintf and also next if/unless :) Although I still haven't tried map, which I will do next. Thank you all!

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Re^5: column counter and printf question
by GotToBTru (Prior) on Oct 29, 2015 at 14:45 UTC

Although one more question, should (@columns-3) maybe be ($columns-3)?

You're thinking of $#columns, which is the index of the last element in the array.

@a = (1, 2, 3);
$count = @a;
printf "\$#a: %d versus \@a in scalar context: %d\n",$#a,$count;
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$#a is 2 versus @a in a scalar context is 3
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Dum Spiro Spero

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