CODEWITHSUNDEEP
perl
user1987607
user1987607

Reputation: 2157

perl - push unique elements into array and create variables from the unique elements

I'm working in Perl.

I start from a tab-delimited txt file with two columns.

cat1    val1
cat1    val2
cat2    val3 
cat3    val4
cat1    val5
cat4    val6

I want to push the unique categories from column 1 into an array & create empty variables that have the same name as these unique categories

so at the end I would have:

@unique_categories = ("cat1", "cat2", "cat3", "cat4");

$cat1 = '';
$cat2 = '';
$cat3 = '';
$cat4 = '';

This is what I've tried:

#! /usr/bin/perl
use strict;
use warnings;

open(my $file,'<',"file.txt") || die ("Could not open file $!"); #input file

my $categories = '';
my @categories_unique = '';

while(<$file>){
    chomp;
    my $line = $_;
    my @elements = split ("\t", $line);
    $categories = $elements[0]; #everything seems fine until here
    push(@categories_unique, $categories) unless grep{$_ eq $categories} @categories_unique; #with this line I want to store the unique values in an array
    #here I want to create the empty variables, but don't know how to
}

Upvotes: 0

Views: 653

Answers (2)

choroba
choroba

Reputation: 242383

Having variables with dynamically created names is dangerous, see Why it's stupid to `use a variable as a variable name' and A More Direct Explanation of the Problem.

In Perl, you can use a hash to both keep the unique values, and also instead of the variables of unknown names. It's also much faster then iterating the whole array every time.

#! /usr/bin/perl
use strict;
use warnings;

open my $fh, '<', 'file.txt' or "Could not open file $!";
my %categories;

while (my $line = <$fh>) {
    chomp $line;
    my @elements = split /\t/, $line;
    ++$categories{ $elements[0] };
}
my @categories = keys %categories;

Right now, the values of the %categories hash is simply the number of times that category is present. For example, $categories{cat1} is 3. If you decide you want the values for each category instead, it's simply a question of replacing 

++$categories{ $elements[0] };

with

push @{ $categories{ $elements[0] } }, $elements[1];

Upvotes: 4

JGNI
JGNI

Reputation: 4013

Not a bad first attempt. here's what you need

#! /usr/bin/perl
use strict;
use warnings;

open(my $file,'<',"file.txt") || die ("Could not open file $!"); #input file

my %categories_unique = ();
my @categories_unique = ();

while(<$file>){
    chomp;
    my $line = $_;
    my @elements = split ("\t", $line);
    $categories = $elements[0]; #everything seems fine until here
    $categories_unique{$categories} = 1; # Use the fact that keys in a hash are unique
}

@categories_unique = keys %categories_unique;
{
    no strict 'refs'; # allows access to symbol table
    *{$_} = undef() foreach @categories_unique; create a symbol table entry 
}

Upvotes: -1

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