Converting an array of hashrefs into a hashref of arrays

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

I've got some data in a database table like this:

[cams] users> SELECT *, DAY(stats_date) as stats_day FROM stream_updat
+e_stats_daily WHERE MONTHNAME(stats_date)='March' AND YEAR(stats_date
+)=2006 ORDER BY DAY(stats_date) LIMIT 3\G
*************************** 1. row ***************************
       stats_date: 2006-03-01
    diary_entries: 2
  photos_uploaded: 0
  videos_uploaded: 0
 stream_questions: 0
             msgs: 12
     date_entered: 2006-03-27 17:32:28
messages_received: NULL
        stats_day: 1
*************************** 2. row ***************************
       stats_date: 2006-03-02
    diary_entries: 7
  photos_uploaded: 0
  videos_uploaded: 0
 stream_questions: 0
             msgs: 4
     date_entered: 2006-03-27 17:35:43
messages_received: NULL
        stats_day: 2
*************************** 3. row ***************************
       stats_date: 2006-03-03
    diary_entries: 2
  photos_uploaded: 0
  videos_uploaded: 0
 stream_questions: 0
             msgs: 2
     date_entered: 2006-03-27 17:42:10
messages_received: NULL
        stats_day: 3
3 rows in set (0.01 sec)

[cams] users>
[download]

and I have the ability to turn this data into a Perl array of hashrefs, with one array element for database row:

@ar = (
 { stats_date => '2006-03-01', diary_entries => 2, msgs => 12, stats_d
+ay => 1},
 { stats_date => '2006-03-02', diary_entries => 7, msgs => 4,. stats_d
+ay => 2},
 { stats_date => '2006-03-03', diary_entries => 3, msgs => 2,. stats_d
+ay => 3},
);
[download]

But the issue is, I need a hashref of arrays so that this data can be properly displayed:

{ 
  diary_entries => [ 2,  7, 3],
  msgs          => [ 12, 4, 2]
}
[download]

I thought there was a CPAN module that did this sort of thing but I can't recall the name of it.

Comment on Converting an array of hashrefs into a hashref of arrays Select or Download Code

Replies are listed 'Best First'.
Re: Converting an array of hashrefs into a hashref of arrays by ikegami (Patriarch) on Mar 28, 2006 at 17:45 UTC
`my %by_fields; #while (my $row = $sth->fetchrow_hashref()) { foreach my $row (@ar) { foreach my $field (keys %$row) { my $value = $row->{$field}; push(@{$by_fields{$field}}, $value); } }` [download]	[reply] [d/l]
Re: Converting an array of hashrefs into a hashref of arrays by bowei_99 (Friar) on Mar 28, 2006 at 20:56 UTC
I think the module you may be referring to is Data::Dumper, although it tends to format it a little differently. You could have something like: `use Data::Dumper; ...your code here ... print Dumper($ref);` [download] where $ref is a reference to your data structure, in this case, a hash of arrays. It's included by default on at least perl 5.6 and above; maybe even earlier versions, so you shouldn't have to install it. -- Burvil	[reply] [d/l]

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