in reply to 'group by query' from array of hashes

I think you need to use the syntax that forces types to arrays and hashes. It's in the Hashes of Arrays section of Chapter 9, Data Structures in the Camel book.

my %queries_by_key = (); # Hash of arrays

my $number_of_queries = scalar @all_queries;

for (my $i = 0 ; $i < $number_of_queries; ++$i) {
    my %query = %{ pop @all_queries }; # value of pop() is a hash

    foreach my $query_key (keys %query) {
        # Treat each value in %queries_by_key as an anonymous array
        push @{ $queries_by_key{$query_key} }, $query{$query_key};
    }
}

foreach my $key (sort keys %queries_by_key) {
     print "$key has ";
     print join ',', @{ $queries_by_key{$key} }; # treat as an array 
     print "\n";
}

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I tried to make this clear, but the syntax is kinda confusing. Hopefully they'll explain it better in the book.

Hope this helps,

Chris

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Re^2: 'group by query' from array of hashes
by Jim (Curate) on Jan 29, 2011 at 16:36 UTC

    Here's my refactoring of chayashida's fine illustration:

    #!perl

use strict;
use warnings;

my @all_queries; # Array of hashes
my %queries_by;  # Hash of arrays

push @all_queries, { foo => 20 };
push @all_queries, { bar => 30 };
push @all_queries, { foo => 10 };
push @all_queries, { zen => 90 };
push @all_queries, { zen =>  1 };

for my $query (@all_queries) {
    my ($query_key, $query_value) = %$query;

    push @{ $queries_by{$query_key} }, $query_value;
}

for my $query_key (sort keys %queries_by) {
    my @query_values = sort { $a <=> $b } @{ $queries_by{$query_key} }
+;
    my $query_values = join ',', @query_values;

    print "$query_key has $query_values\n";
}

__END__
bar has 30
foo has 10,20
zen has 1,90

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