How do I access array of hash in perl?

Question

I have a big array of hashes, I want to grab some hash from the array and insert into new array without changing the first array. I am having problem pushing the hash to array, how do I access the ith element which is a hash.

my @myarray;
$my_hash->{firstname} = "firstname";
$my_hash->{lastname} = "lastname";
$my_hash->{age} = "25";
$my_hash->{location} = "WI";
push @myarray,$my_hash;

$my_hash->{firstname} = "Lily";
$my_hash->{lastname} = "Bily";
$my_hash->{age} = "22";
$my_hash->{location} = "CA";
push @myarray,$my_hash;

$my_hash->{firstname} = "something";
$my_hash->{lastname} = "otherthing";
$my_hash->{age} = "22";
$my_hash->{location} = "NY";
push @myarray,$my_hash;

my @modifymyhash;
for (my $i=0;$i<2; $i++)  {
        print "No ".$i."\n";
        push (@modifymyhash, $myarray[$i]);
        print "".$myarray[$i]."\n";  #How do I print first ith element of array which is hash.
 }

Community · Accepted Answer · 2017-05-23 12:02:48Z

14

First you should

use strict;
use warnings;

then define

my $my_hash;

initialize $my_hash before you assign values, because otherwise you overwrite it and all three elements point to the same hash

$my_hash = {};

and finally, to access the hash's members

$myarray[$i]->{firstname}

or to print the whole hash, you can use Data::Dumper for example

print Dumper($myarray[$i])."\n";

or some other method, How can I print the contents of a hash in Perl? or How do I print a hash structure in Perl?

Update to your comment:

You copy the hashes with

push (@modifymyhash, $myarray[$i]);

into the new array, which works perfectly. You can verify with

foreach my $h (@myarray) {
    print Dumper($h), "\n";
}

foreach my $h (@modifymyhash) {
    print Dumper($h), "\n";
}

that both arrays have the same hashes.

If you want to make a deep copy, instead of just the references, you can allocate a new hash and copy the ith element into the copy. Then store the copy in @modifymyhash

my $copy = {};
%{$copy} = %{$myarray[$i]};
push (@modifymyhash, $copy);

edited May 23, 2017 at 12:02

CommunityBot

11 silver badge

answered Mar 19, 2013 at 21:01

Olaf Dietsche

74.4k9 gold badges113 silver badges214 bronze badges

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

2 Comments

mysteriousboy Over a year ago

I have used both string and warnings. And I have initialize and define my_hash as well. I want to push the whole hash into new array. Thanks anyway.

Olaf Dietsche Over a year ago

@mysteriousboy You have already pushed the hashes into @modifymyhash. What's wrong with that?

choroba · Accepted Answer · 2013-03-19 21:02:11Z

2

To dereference a hash, use %{ ... }:

print  %{ $myarray[$i] }, "\n";

This probably still does not do what you want. To print a hash nicely, you have to iterate over it, there is no "nice" stringification:

print $_, ':', $myarray[$i]{$_}, "\n" for keys %{ $myarray[$i] };

answered Mar 19, 2013 at 21:02

choroba

245k27 gold badges221 silver badges304 bronze badges

Collectives™ on Stack Overflow

How do I access array of hash in perl?

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related