Selective Printing of Lines

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

Hi I have a file with data like this.

-1 2 ereu
1 2 rerer
2 2 rere
3 2 eee
3 2 wwwe
9 2 qqewew
9 2 vvvgf
-1 2 wwwew
4 3 wwew
-9 3 wwss
6 3 jjuu
7 3 kkii
7 3 ggtyu
8 3 ffder
1 4 rrtrr
1 4 rree
[download]

If the values in 2nd column are same, calculate the minimum value in the first column and print corresponding lines. My desired output is;

-1 2 ereu
-1 2 wwwew
-9 3 wwss
1 4 rrtrr
1 4 rree
[download]

I wrote a code like this.

#! usr/bin/perl
use warnings;
use strict;
my @a = <> ;
my @b = ();
foreach (@a) {
 push (@b, split(/ /));
             }
my $i = 0;
my $j = 1;
my $min = $b[0];
my $x = 0;
while ($x++ < 150) {
    $j = $j+3;
    $i = $i+3;
 
        if ($b[$j] = $b[$j+3]) {

          if ($min > $b[$i]) {
                                   
                    $min = $b[$i]
                             }
                         
                               }
                   }

 print "$min\n";
[download]

But the code ignores the condition if ($b$j = $b$j+3) and prints just the minimum value of first column. My idea was to use a regex involving the minimum value to print the corresponding lines. Obviously I am a newbie to Perl. Can experts help me please? thanks in advance.

Comment on Selective Printing of Lines Select or Download Code

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Re: Selective Printing of Lines by ambrus (Abbot) on Sep 16, 2011 at 09:09 UTC
But the code ignores the condition `if ($b[$j] = $b[$j+3])` That's because `=` does assignment, not comparison.	[reply] [d/l] [select]
Re: Selective Printing of Lines by onelesd (Pilgrim) on Sep 15, 2011 at 22:31 UTC
Had a beer at lunch and don't feel like doing my own work... `use strict ; use warnings ; my @data = sort <DATA> ; my %min ; foreach (@data) { my ($col1, $col2, $col3) = split /\s+/, $_ ; $min{$col2} = $col1 if (! defined $min{$col2}) ; print $_ if ($col1 eq $min{$col2}) ; } __DATA__ -1 2 ereu 1 2 rerer 2 2 rere 3 2 eee 3 2 wwwe 9 2 qqewew 9 2 vvvgf -1 2 wwwew 4 3 wwew -9 3 wwss 6 3 jjuu 7 3 kkii 7 3 ggtyu 8 3 ffder 1 4 rrtrr 1 4 rree` [download]	[reply] [d/l]
Re^2: Selective Printing of Lines by polsum (Novice) on Sep 16, 2011 at 00:24 UTC
THank you all for excellent replies. All of them are working fine and now I am trying to 'decode' each of them :D. Hi onelesd, Can you please explain the `if (! defined $min{$col2})` part of your code. Ever since you posted this code, I have been banging my head to understand the usage of defined and the unary operator !. Thanks in advance.	[reply] [d/l]
Re^3: Selective Printing of Lines by onelesd (Pilgrim) on Sep 16, 2011 at 04:28 UTC
See: perldoc -f defined `defined EXPR defined Returns a Boolean value telling whether EXPR has a valu +e other than the undefined value "undef".` [download] ! negates the condition, so in natural language the condition is: "`if $min{$col2} is not defined`".	[reply] [d/l] [select]
Re: Selective Printing of Lines by Kc12349 (Monk) on Sep 15, 2011 at 22:40 UTC
What is this use case here? Something beyond homework? my %min_data; for my $line (@lines) { my @columns = split ' ', $line; unless (exists $min_data{$columns[1]}) { $min_data{ $columns[1] } = {min=>$columns[0],lines=>[$line]}; } elsif ($columns[0] == $min_data{ $columns[1] }->{min}) { push @{ $min_data{ $columns[1] }->{lines} }, $line; } elsif ($columns[0] < $min_data{ $columns[1] }->{min}) { $min_data{ $columns[1] }->{lines} = [$line]; $min_data{ $columns[1] }->{min} = $columns[0]; } } for my $column_two (sort keys %min_data) { say for @{ $min_data{$column_two}->{lines} }; } [download] onelesd's solution is far more simple	[reply] [d/l]
Re^2: Selective Printing of Lines by onelesd (Pilgrim) on Sep 15, 2011 at 23:01 UTC
Hopefully the teacher gives us both an `A+`	[reply] [d/l]
Re: Selective Printing of Lines by Anonymous Monk on Sep 15, 2011 at 23:05 UTC
Wish I had a beer... `#!/usr/bin/perl use v5.12; use warnings; use strict; my %data; while (<DATA>) { my ($num, $key) = split; if (my $min = $data{$key}) { no warnings 'numeric'; $data{$key} .= $_ if $num == $min; $data{$key} = $_ if $num < $min; } else { $data{$key} = $_; } } print $data{$_} for sort keys %data; __END__` [download]	[reply] [d/l]