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

Why does this only print the group name and not the values or members of @vars?
my %hash;

open (DATA, "<data.csv") or die "Can't open file $!\n";
my @DATA = <DATA>;
close (DATA);

foreach my $rec (@DATA) {
  chomp $rec;
  my @vars = split(/,/,$rec);
   if ($vars[0]) {
      map  $_ =~ s/\s+$//g, @vars;
      
      #hash3 used for comparing comp_name values
      $hash3{$vars[2]} = (@vars[0,1]); #add 1,2,3 as needed
  }
}

foreach my $alias (keys %hash3) {
    print "The members of $alias are\n";
    foreach (@{$hash3{$alias}}) {
        print "\t$_\n";
    }
}

[download]

qball~"I have node idea?!"

Replies are listed 'Best First'.
Re: Values not printing.
by ton (Friar) on Apr 13, 2001 at 00:49 UTC
    Because of this line: 
    $hash3{$vars[2]} = (@vars[0,1]); #add 1,2,3 as needed

    [download]
    The expression on the left is in scalar context. Thus, the array on the right is evaluated in scalar context, so you store the size of the array, not the elements. Try using this line instead: 
    @{$hash3{$vars[2]}} = (@vars[0,1]); #add 1,2,3 as needed

    [download]
    UPDATE: As sierrathedog04 notes, it is the last element of the list that was previously stored, not the size.

    -Ton
    -----
    Be bloody, bold, and resolute; laugh to scorn
    The power of man...

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      In the program as qball originally wrote it, 
      $hash3{$vars[2]} = (@vars[0,1]);

      [download]
      stores the value of $vars[1] rather than the size of @vars[0,1]

      You can test this yourself by placing a print $hash3{$vars[2]} , "\n"; underneath the line that qball originally wrote.

      (@vars[0,1]) is a list but not an array. When perl evaluates a list in scalar context it usually throws out everything except for the last element. The last element of the slice @vars[0,1] is $vars[1]. Hence, that is what perl stores.

      The distinction between scalar and list contexts, and the implicit overloading of the two by most functions, is one of the key and distinctive elements of Perl. It may be that the genius of Larry Wall, and the success of Perl, all comes down to that critical distinction.

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      ton, that worked perfectly. Thank you.

      How would I access the elements of each array for each key?

      qball~"I have node idea?!"
[reply]
        You already are: 
        foreach my $alias (keys %hash3) {
    print "The members of $alias are\n";
    foreach (@{$hash3{$alias}}) {
        print "\t$_\n";
    }
}

        [download]
        If you didn't want to use foreach's aliasing, you would do something like:
        print $hash3{$hashKey}->[$arrayIndex];

        [download]
        -Ton
        -----
        Be bloody, bold, and resolute; laugh to scorn
        The power of man...
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[d/l]
[select]
Re: Values not printing.
by qball (Beadle) on Apr 13, 2001 at 19:14 UTC
    I modifed the original code as follows:
    my %hash;

open (DATA, "<data.csv") or die "Can't open file $!\n";
my @DATA = <DATA>;
close (DATA);

foreach my $rec (@DATA) {
  chomp $rec;
  my @vars = split(/,/,$rec);
  if ($vars[0]) {
      map  $_ =~ s/\s+$//g, @vars;
      
      #hash3 used for comparing comp_name values
      #added join to [ton]'s modification
      @{$hash3{$vars[2]}} = join(',',@vars[0,1,2]);
  }
}

#modified formatting as well
foreach my $alias (keys %hash3) {
    print "\nThe members of $alias are: ";
    foreach (@{$hash3{$alias}}) {
        print "$_";
    }
}

    [download]
    Now that I can print each key and its array values delimited by commas, how woulc I access each value? For example, suppose I want to insert @vars[1] into a database, how would I access @vars[1] within hash3?

    qball~"I have node idea?!"
[reply]
[d/l]
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