Create an array for key value in hash (Perl)

Question

I am having a very small difficulty in Perl.

I am reading a text file which for some information. While I read the text file, I select some keys from text; as I read further, I wish to save an array of values for the keys.

See for e.g.

Alpha 1

Something: 2132
Something: 2134

Alpha 2

Something: 2132
Something: 2134

I read the file into an array called lines:

my $h;
my $alpha;
for my $line (@lines){
    if ($line =~ m/Alpha (\d+)/){
        $alpha = $1;
        $h->{$alpha} = (); # create empty array for key?
    }
    elsif ($line =~ m/Something: (\d+)/){
        push($h->{$alpha}, $1);
    }
}

Apparently, it gives me an error:

Type of arg 1 to push must be array (not hash element) at test.pl line 28, near "$1)"
Execution of test.pl aborted due to compilation errors.

Unable to figure this out.

Guru · Accepted Answer · 2013-03-07 05:20:23Z

4

A hash key value can contain only a scalar. If you want to store an array, then you need to go for array reference.

You can do something like this:

for my $line (@lines){
    if ($line =~ m/Alpha (\d+)/){
        $alpha = $1;
        $h->{$alpha} = []; # create empty array refernece for key
    }
    elsif ($line =~ m/Something: (\d+)/){
        push( @{$h->{$alpha}}, $1);
    }
}

answered Mar 7, 2013 at 5:20

Guru

17.1k2 gold badges37 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

p0lAris Over a year ago

Oh great. I've understood it now. Thanks.

Krishnachandra Sharma Over a year ago

Testcase: $alpha may remain undef. Shouldn't that be taken care of?

Jim Garrison · Accepted Answer · 2013-03-07 05:21:23Z

3

You need to make two changes:

    $h->{$alpha} = [];
                   ** - Create an anonymous array and store 
                        a ref to it in the hash

And

    push(@{$h->{$alpha}}, $1);

because push requires an actual array, and you have an array reference. The @{...} wrapper dereferences the arrayref to an actual array.

answered Mar 7, 2013 at 5:21

Jim Garrison

87k20 gold badges162 silver badges197 bronze badges

Comments

Krishnachandra Sharma · Accepted Answer · 2013-03-07 06:04:35Z

0

As earlier answers say, they are correct. But not perfect. $alpha may remain undef. Hence in order to avoid it please add a check.

my $alpha;
for my $line (@lines){
    if ($line =~ m/Alpha (\d+)/){
        $alpha = $1;
        $h->{$alpha} = []; # create empty array refernece for key
    }
    elsif ($line =~ m/Something: (\d+)/){
        if(defined $apha) { ## Check
           push( @{$h->{$alpha}}, $1);
        }
    }
}

answered Mar 7, 2013 at 6:04

Krishnachandra Sharma

1,3503 gold badges20 silver badges43 bronze badges

Collectives™ on Stack Overflow

Create an array for key value in hash (Perl)

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related