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Setting up a hash of lists
More than Simple Lists and Hashes! example from a Well House Consultants training course
More on More than Simple Lists and Hashes! [link]

This example is described in the following article(s):
   • Setting up a matrix of data (2D array) for processing in your program - [link]

Source code: rain Module: P217

=head1 A Hash of lists

A common requirement is to read in a data file where each
line is a record of multiple fields and create a structure
in memory to hold that data, split down so that it can be
processed. Here's an example - a hash of lists


# Data is build into this teaching example rather than
# bring a separate file (keeps it all together for training)

$info = <<ABOUT;
Cambridge Flat City
Norwich Boring City
Norwich Alabamish City
Norwich Fuuny Virtual
Lakenheath Military Village
Thetford Forest Town
Norwich New York Burb
London Big City

# Read through each line of the data
# Take off the first field as the key
# Make the key unique (just in case two were identical)
# Add the list into the hash based on the (modified) key

foreach $line(split(/\n/,$info)) {
        my ($place,@fields) = split(/\t/,$line);
        $place .= "_" while ($records{$place});
        $records{$place} = \@fields;

# Demonstration to show how we can pass the whole
# structure into a sub, just by passing a single address

sub shoutabout {
        $inparam = $_[0];
        for $k (keys(%$inparam)) {
                $$inparam{$k}[0] .= " on Friday";

print ${$records{"Norwich"}}[0],"\n";
print $records{"Norwich"}->[0],"\n";
print $records{"Norwich"}[0],"\n";

for $pk (grep(/^Norwich_*$/,keys %records)) {
        $pkp = $pk;
        $pkp =~ s/_+//;
        print "$pkp ...>> ",$records{$pk}[0],"\n";


Sample output

wizard:csr2 graham$ perl rain
Boring on Friday
Boring on Friday
Boring on Friday
Norwich ...>> Fuuny on Friday
Norwich ...>> Alabamish on Friday
Norwich ...>> Boring on Friday
Norwich ...>> New York on Friday
wizard:csr2 graham$

Learn about this subject
This module and example are covered on the following public courses:
 * Perl Programming
 * Perl for Larger Projects
 * Perl bootcamp
 * Learning to program in Perl
 * Perl Programming
Also available on on site courses for larger groups

Books covering this topic
Yes. We have over 700 books in our library. Books covering Perl are listed here and when you've selected a relevant book we'll link you on to Amazon to order.

Other Examples
This example comes from our "More than Simple Lists and Hashes!" training module. You'll find a description of the topic and some other closely related examples on the "More than Simple Lists and Hashes!" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
• Our Solutions centre provides a number of longer technical articles.
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