http://qs321.pair.com?node_id=780174


in reply to Re^2: Array to hash converstion
in thread Array to hash converstion

I believe this is your question:
"I have an array (@data_list) containing hash references. Each hash reference contains two keys, 'key' and 'value'. I want to turn this into one hash containing 'key'=>'value' pairs. How can I do this?"

My solutions below assume that you have unique key values, or are un-interested in collisions. In the case of a collision, the last reference to the key wins.

Here is a fully verbose version: 

my %final_hash;
foreach my $data_pair ( @data_list)
{
  $key   = $data_pair->{ key };
  $value = $data_pair->{value};
  $final_hash{ $key } = $value;
}

use Data::Dumper;
print Dumper \%final_hash;

[download]

A shorter version: 

my %final_hash = 
  map { $_->{key} => $_->{value} } 
  @data_list;

#verify the output
use Data::Dumper;
print Dumper \%final_hash;

[download]
And how do we know they work? We test them.

Full version with tests: 

#!/usr/bin/perl -w

use strict;
use Data::Dumper;
use Test::More tests => 2;

my @data_list = (
    { key => 'correct',    value => 'AAA' },
    { key => 'correction', value => 'BBB' },
    { key => 'date',       value => '20090303' },
    { key => 'date',       value => '20090308' },
);
my $expected = {
    correct    => 'AAA',
    correction => 'BBB',
    date       => '20090303',
    date       => '20090308',
};

my %final_hash_long;
foreach my $data_pair (@data_list) {
    my $key                = $data_pair->{key};
    my $value              = $data_pair->{value};
    $final_hash_long{$key} = $value;
}

my %final_hash_short =
  map { $_->{key} => $_->{value} } @data_list;

is_deeply( \%final_hash_long,  $expected, "long version works" );
is_deeply( \%final_hash_short, $expected, "short version works" );

[download]

Replies are listed 'Best First'.
Re^4: Array to hash converstion
by gem555 (Acolyte) on Jul 15, 2009 at 07:03 UTC 
    #!/usr/bin/perl -w
use strict;

my @value_pairs = qw (one abc two xyz);
my %hash = @value_pairs;

foreach my $key (keys %hash)
{
   print "key $key is $hash{$key}\n";
}
__END__
prints:
key one is abc
key two is xyz
key one is def

    [download]
    If two keys are same then, output is 
    key one is abc
key two is xyz

    [download]
    so for the key one value is def is not printed here. The expected output is 
    key one is abc
key two is xyz
key one is def

    [download]
    Please tell me how can I get the output like this
[reply]
[d/l]
[select]
      The issue you've run into here is that each hash key can only be associated with a single value, so the second assignment to $hash{one} overwrites its previous value. Or, as spazm put it in the comment you were replying to,
      My solutions below assume that you have unique key values, or are un-interested in collisions. In the case of a collision, the last reference to the key wins.
      However, the single value held by the hash doesn't have to be a simple scalar. If you use an array reference there (giving you a "hash of arrays" or "HoA"), then the code will be a little more complex, but you'll be able to store as many values as you like with each key: 
      #!/usr/bin/perl

use strict;
use warnings;

my @value_pairs = qw( one abc two xyz one def );
my %hash;

while (@value_pairs) {
  my $key = shift @value_pairs;
  my $value = shift @value_pairs;
  push @{$hash{$key}}, $value;
}

for my $key (keys %hash) {
  print "key $key has values: ", join(', ', @{$hash{$key}}), "\n";
}
__END__
key one has values: abc, def
key two has values: xyz

      [download]
[reply]
[d/l]
[select]
         
$correction = $data_pair->{value} if($data_pair->{key} eq 'correct');

        [download]
        how to store the value in $correction only if the $data_pair->{value} is not empty.
[reply]
[d/l]
Re^4: Array to hash converstion
by gem555 (Acolyte) on Jul 16, 2009 at 10:40 UTC 
    #!/usr/bin/perl -w
use strict;
use warnings;

my @data_list = (
    {key => 'correct', value => 'Article_text1'},
    {key => 'correct', value => 'Article_text2'},
    {key => 'date', value => '2009-01-01'},
    {key => 'date', value => '2009-01-02'}
);


my @correct;
my @date;
for my $data_pair (@data_list) {
print "Value:$data_pair->{value}:Key:$data_pair->{key}\n";

if($data_pair->{key} eq 'correct'){
 @correct = $data_pair->{value};
}


if($data_pair->{key} eq 'date'){

 @date = $data_pair->{value};
}


}
print "The array is @correct\n";
print "The array is @date\n";

    [download]
    The array stores only the last value. How to store all the values into array
[reply]
[d/l]

In Section Seekers of Perl Wisdom