Hash slice from a hashref

Random_Walk has asked for the wisdom of the Perl Monks concerning the following question:

Good $localtime honoured monks

I am having a little bother getting a hash slice from an anonymous hash to which I only have a reference. Without further ado some code

#!/usr/bin/perl -l
# this works OK
my @l=qw(this is);
my %e=qw( this 7 is 6 then 9);
print $e{is};
print join "+", @e{@l}
# output
6
7+6

#!/usr/bin/perl
# yet all my attempts to get this working failed
# I tried @{$r->{@l}} @{$r->{@l}} and many more I forget
my @l=qw(this is);
my $r={qw( this 7 is 6 then 9)};
print $r->{is};
print join "+", @{$r->{@l}}
# output
6

# just a blank line above.
[download]

What arcane combination of line noise like sigils will bring me enlightenment ?

Cheers,
R.

Pereant, qui ante nos nostra dixerunt!

Comment on Hash slice from a hashref Download Code

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Re: Hash slice from a hashref by davorg (Chancellor) on Sep 07, 2006 at 13:52 UTC
`print join "+", @{$r}{@l}` [download] The general rule is that when dealing with references you can replace a hash name with {$ref}. So @hash{@keys} becomes @{$ref}{@keys}. -- <http://dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply] [d/l]
Re: Hash slice from a hashref by Fletch (Bishop) on Sep 07, 2006 at 13:51 UTC
Erm, `@{$r->{@l}}` is treating the value in `$r->{@l}` as an arrayref (which isn't going to do anything useful). You mean `@{ $r }{ @l }`.	[reply] [d/l] [select]
Re^2: Hash slice from a hashref by Random_Walk (Prior) on Sep 07, 2006 at 13:57 UTC
Thanks, I realised it was not going to do anything useful but the required syntax had elluded me completely. Now it is working a treat and I can get some really ugly coding tidied up. Cheers, R. Pereant, qui ante nos nostra dixerunt!	[reply] [d/l]
Re: Hash slice from a hashref by VSarkiss (Monsignor) on Sep 07, 2006 at 14:02 UTC
The coolest cheat sheet I know for this is tye's References quick reference. All you wanted to know and more! Do not rebuke them with harsh words ... but rather lead them gently - with URLs - so that they may learn wisdom.	[reply]
Re^2: Hash slice from a hashref by planetscape (Chancellor) on Sep 07, 2006 at 15:25 UTC
Indeed. :-) busunsl's intro to references is also quite useful. IMHO, one of the best discussions of complex data structures, and how to access their innards (using slices and so on), is to be found in Chapter 3. References and complex data structures of `perlinter.pdf`, available from Perl Training Australia. The OP would probably want the most current version of the course notes, though, which have been reworked into `progperl.pdf`, available from the same page noted above. HTH, planetscape	[reply] [d/l] [select]