References :: Array of Hashes

Dynamically creating complex data structures during an iterative process is often required and quite easy. Accessing values (iteratively or otherwise) from a complex data structure can be an overwhelmingly pleasant experience.

Generating an Array of Hashes (AoH)

This structure is very common, representing rows extracted from either a text file of columnar data or from an SQL query.

example text file contents:

J.S. Bach, Baroque, 0 Brahms, Romantic, 4 Haydn, Classical, 104 Prokofiev, 20th Century, 7 Schubert, Romantic, 9 Sibelius, 20th Century, 7 Vaughan Williams, 20th Century, 9

 1        # declare empty array reference to store our records
 2        my $composers = [];
 3
 4        # parse the file and create array of hashes
 5        while (<IN>)
 6        {
 7            my ($name, $period, $num) = split(/,\s*/, $_);
 8
 9            # push anonymous hash reference onto the array reference
10            push(@{$composers}, { name => $name, period => $period, num => $num });
11        }

Accessing an Array of Hashes

Any of the values of the data structure $composers can be easily accessed. Who is the composer in the second element of the array?

 1        print $composers->[1]->{'name'};
 2
 3        # outputs 'Brahms'

And what is the composer's musical period?

 1        print $composers->[1]->{'period'};
 2
 3        # outputs 'Romantic'

Let's print out all composers' names except those from the Romantic period:

 1        # curly braces are optional
 2        for my $record (@{$composers})
 3        {
 4            next if $record->{'period'} =~ /Romantic/o;
 5
 6            print qq[$record->{'name'}\n];
 7        }