Hash of arrays in Perl

One key, many values: the workhorse structure for grouped data.

use strict;
use warnings;

my %tags = (
    perl   => ["regex", "sigils"],
    python => ["indent"],
);

# push through the reference grows the inner array
push @{ $tags{perl} }, "context";
push @{ $tags{python} }, "batteries";

for my $lang (sort keys %tags) {
    my $count = scalar @{ $tags{$lang} };
    print "$lang ($count): @{ $tags{$lang} }\n";
}

How it works

1. Each value in %tags is an anonymous array built with [...].
2. push @{ $tags{perl} } grows the inner array through its reference.
3. The loop interpolates @{ $tags{$lang} } to print each list in place.

Keywords and builtins used here

• for
• keys
• my
• print
• push
• scalar
• sort
• use

The run, in numbers

Lines

16

Characters to type

338

Tokens

84

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 78 seconds.

Type this snippet

Step 2 of 3 in References & structures, step 20 of 27 in Language basics.

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