Re: Using an element in a Hash of Arrays to access the key

[tybalt89]

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1185923

use strict;
use warnings;

my @array1 = ("one", "two", "three", "four", "five");
my @array2 = ("banana", "pear", "apple");

my %hash = (
    numbers => \@array1,
    fruit => \@array2
);

# make a reverse lookup hash

my %reverse;
for my $key (keys %hash)
  {
  push @{ $reverse{$_} }, $key for @{ $hash{$key} };
  }

# then do direct lookup ( you may get multiple values, or none )

print "banana -> @{ $reverse{'banana'} // [] }\n";

[orangepeel1]

Thank you, this worked. Could you clarify what the purpose of  // [] is in  print "banana -> @{ $reverse{'banana'} // [] }\n";?

[tybalt89]

That is there to handle the case when the element you are trying to look up does not exist.
Try looking up 'peach' with and without that part of the code.