Question

Say I have a hash that I can index as:

$hash{$document}{$word}

From what I read online (although I could not find this on perlreftut, perldsc or perllol), I can slice a hash using a list if I use the @ prefix on my hash to indicate that I want the hash to return a list. However, if I try to slice my hash using a list @list:

@%hash{$document}{@list}

I get several "Scalar values ... better written" errors.

How can I slash a nested hash in Perl?

Answer 1

The sigill for your hash must be @, like so:

@{$hash{$document}}{@list}

Assuming @list contains valid keys for %hash it will return the corresponding values, or undef if the key does not exist.

This is based on the general rule of a hash slice:

%foo = ( a => 1, b => 2, c => 3 );
print @foo{'a','b'};               # prints 12
%bar = ( foo => \%foo );           # foo is now a reference in %bar
print @{ $bar{foo} }{'a','b'};     # prints 12, same data as before