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

Hi, Monks! I am trying to creat a series of arrays whose names are the values of a series of scalars. Here is the code:

while(<FGLCS>){
chomp;
($scfd_name_frgt,$stt_pst_frgt,$stp_pst_frgt,$lgh_frgt)=split /\t/,$_;
$scfd_name_frgt=reverse $scfd_name_frgt;
unless($scfd_name_frgt eq $scfd_name_frgt_tmp){
$scfd_name_frgt_tmp=$scfd_name_frgt;
@{$scfd_name_frgt}=($stt_pst_frgt,$stp_pst_frgt,$lgh_frgt);
$frgtlocs{$scfd_name_frgt}=\@{$scfd_name_frgt};
}
else{
push @{$frgtlocs{$scfd_name_frgt}},($stt_pst_frgt,$stp_pst_frgt,$lgh_f
+rgt);
}
}

[download]

I wish to creat the arrays whose names are the values of the scalars "$scfd_name_frgt". But under "use strict", @{$scfd_name_frgt} is defined as dereference of reference of $scfd_name_frgt. How can I name arrays via scalars values under "use strict" ?

Replies are listed 'Best First'.
Re: How to name arrays via scalars.
by AnomalousMonk (Archbishop) on May 03, 2014 at 09:29 UTC

    Why it's stupid to `use a variable as a variable name'

    Update: 

    c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"use warnings;
 use strict;
 ;;
 my $foo = 'bar';
 ;;
 my %data;
 push @{ $data{$foo} }, qw(zero one two three);
 dd \%data;
 ;;
 print qq{'$data{$foo}[1]'};
"
{ bar => ["zero", "one", "two", "three"] }

'one'

    [download]

[reply]
[d/l]

      Thanks for you advice. It is very helpful.

[reply]
Re: How to name arrays via scalars.
by hdb (Monsignor) on May 03, 2014 at 10:04 UTC

    Due to a feature of Perl called Autovivification, you only need this: 

    use strict;
use warnings;

while(<FGLCS>){
  chomp;
  my ($scfd_name_frgt,$stt_pst_frgt,$stp_pst_frgt,$lgh_frgt)=split /\t
+/,$_;
  $scfd_name_frgt=reverse $scfd_name_frgt;
  push @{$frgtlocs{$scfd_name_frgt}},($stt_pst_frgt,$stp_pst_frgt,$lgh
+_frgt);
}

    [download]

    If @{$frgtlocs{$scfd_name_frgt}} does not exist, Perl just creates an array and you are done.

    UPDATE: Also looking at these two lines:

    @{$scfd_name_frgt}=($stt_pst_frgt,$stp_pst_frgt,$lgh_frgt);
$frgtlocs{$scfd_name_frgt}=\@{$scfd_name_frgt};

    [download]

    They can be abbreviated using square brackets to create a reference to an array:

    $frgtlocs{$scfd_name_frgt}=[$stt_pst_frgt,$stp_pst_frgt,$lgh_frgt];

    [download]

    There is no need to create a named array first and then store a reference to it (if that is what you want).

[reply]
[d/l]
[select]

      Thanks very much. Your answer has directly solved my problem. I now understand more about the reference.

[reply]
Re: How to name arrays via scalars.
by Laurent_R (Canon) on May 03, 2014 at 09:58 UTC
    While you can use symbolic references under the use strict; pragma using the additional no strict refs; pragma and global variables, this is very generally considered as a (very) bad idea. It is much better practice to use one more level of reference in your data structure, such as an hash of arrays in your case (if I understand you correctly).
[reply]
[d/l]
[select]

      Yeah, one more level can work. But it just need to be @{$genelocs{$scfd_name_gene}}=($a,$b,$c). Thanks anyway.

[reply]
[d/l]

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