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Re^5: Combining 3 files

by Anonymous Monk
on Jun 27, 2011 at 10:27 UTC ( #911539=note: print w/replies, xml ) Need Help??


in reply to Re^4: Combining 3 files
in thread Combining 3 files

Hi anonymous monk, yes I'm still finding this confusing.

Well hold onto your pants :)

You mentioned it is confusing $dataset for a hashref.

Look at the @beef equivalent example, it is this line that dies with Can't use an undefined value as an ARRAY reference

my @beef = @{ $dataset->{ $col[0] } };
This line is really
my $key = $col[0] ; my $meat = $dataset->{ $key }; my @beef = @{ $meat };
I misspoke when I said it is confusing $dataset for a hashref , in actuality, $dataset is a hashref.

The problem is, $key is not in $dataset, so $meat is undef

Since meat is undef, trying to treat $meat as an array by de-referencing it, triggers a warning if you have warnings on, and triggers an error, if you have strict on.

## no warnings or errors $ perl -e "print @{ undef() }; print 6" 6 ## a warning is issued, but 6 still gets printed $ perl -we "print @{ undef() } Use of uninitialized value in array dereference at -e line 1. 6 ## with strict the warning is fatal, 6 not printed cause program died $ perl -Mstrict -we "print @{ undef() } Can't use an undefined value as an ARRAY reference at -e line 1.
See References quick reference

To avoid this error, you might add

next unless $meat;
You don't want to disable strict :)

Lets take apart a simpler example, one that builds @data

push @{$data[$nr - 1]->{shift(@cols)}},\@cols;
aka
push @{ $data[ $nr - 1 ]->{ shift(@cols) } }, \@cols;
aka
push @{ $data[ $fileCount ]->{ shift @col } }, \@col;
is really
my $Hashref = $data[ $fileCount ]; if( not $Hashref){ $Hashref = $data[ $fileCount ] = {}; } my $key = shift @col; my $Arrayref = $Hashref->{ $key }; if( not $Arrayref ){ $Arrayref = $Hashref->{ $key } = []; } push @{ $Arrayref }, \@col;
or even
my $Hashref = $data[ $fileCount ]; if( not $Hashref){ my %newHashThatIsOnlyNamedHere; $Hashref = $data[ $fileCount ] = \%newHashThatIsOnlyNamedHere; } my $key = shift @col; my $Arrayref = $Hashref->{ $key }; if( not $Arrayref ){ my @newArrayThatIsOnlyNamedHere; $Arrayref = $Hashref->{ $key } = \@newArrayThatIsOnlyNamedHere; } push @{ $Arrayref }, \@col;

Replies are listed 'Best First'.
Re^6: Combining 3 files
by garyboyd (Acolyte) on Jun 27, 2011 at 14:47 UTC

    Thanks for the detailed post. I'm still having problems with the "Use of uninitialized value in array element" error. I adjusted the code, however I'm not sure where I need to insert the equivalent of the

    next unless $meat;

    I can get it to work by commenting out use strict;

    ##!/usr/bin/perl #22/06/2011 use strict; use warnings; use File::Slurp; use Data::Dumper; my @data; my @col; my $dataset; my @fields; my %out; my $Hashref; my $fileCount; my @out; open INFILE, "<Primer-Rev1" or die $!; open my $outfh, '>', "outputfile.txt" or die $!; for my $nr (1..2) { for my $line (read_file('Primer-For'.$nr)) { my @col = split(/\t/,$line); push @{$data[$nr - 1]->{shift(@col)}},\@col; } } while (<INFILE>){ @col = split(/\t+/, $_); chomp (@col); my ($header, $length, $tm, $sequence) = @col[0..3]; # expecting file3 line in @col my @results = ( $col[1], $col[2] ); #print Dumper (\@results) for my $dataset (@data) { my @out = push @{ $data[ $fileCount ]->{ shift @col } }, \@col; #print Dumper (\@data); #} @out = sort { my $diff_a = $col[2] - $a->[1]; $diff_a *= -1 if $diff_a < 0; my $diff_b = $col[2] - $b->[1]; $diff_b *= -1 if $diff_b < 0; $diff_a <=> $diff_b; } @out; print Dumper (\@out); push @results, $out[0]->[2]; } #foreach (@results){ # print $_."\n"} }

      however I'm not sure where I need to insert the equivalent of the

      Next line, right after you initialize $meat

      push @{ $data[ $fileCount ]->{ shift @col } }, \@col;

      Wait a minute, why did you copy that?

        I thought that it was a simplified version of:

        my @beef = @{ $dataset->{ $col[0] } };

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