Beefy Boxes and Bandwidth Generously Provided by pair Networks
There's more than one way to do things

comment on

( [id://3333] : superdoc . print w/replies, xml ) Need Help??

I'm trying to (ab)use hash slices. I understand the typical (@hash{@keys}) use of a slice, but now I'm trying to do something a bit more complex and take a slice of a hash of hashes. Using a slice in a %HoH when the list is provided as the second 'key' is no problem, but can slices be used to cut across the first set of keys as well? I didn't find anything when I searched for this in the docs or on PM.

Perhaps a bit of code will help define the problem:

use strict; use warnings; my @keys = qw( a c ); my %hash = ( a => 1, b => 2, c => 3, d => 4 ); # typical use - no problem # @hash{a,c} is like $hash{a}, $hash{c} print join( ' ', @hash{@keys} ), "\n"; # 1, 3 my %hoh = ( a => { a => 'a1', b => 'a2', c => 'a3', d => 'a4' }, b => { a => 'b1', b => 'b2', c => 'b3', d => 'b4' }, c => { a => 'c1', b => 'c2', c => 'c3', d => 'c4' }, d => { a => 'd1', b => 'd2', c => 'd3', d => 'd4' } ); # typical use expanded to a %HoH - no problem # @{ $hoh{b} }{a, c} is like $hoh{b}{a}, $hoh{b}{c} print join( ' ', @{ $hoh{b} }{@keys} ), "\n"; # b1, b3 # now I want to slice across the first key instead of the second # want something like $hoh{a}{d}, $hoh{c}{d} print join( ' ', @hoh{@keys}{d} ), "\n"; # syntax error # I tried dereferencing the list of hashrefs, but only # the last ref in the list was used ($hoh{c}) print join( ' ', @{ @hoh{@keys} }{d} ), "\n"; # c4 # do I have to resort to this? print join( ' ', map{ $_->{d} } @hoh{@keys} ), "\n"; # a4 c4

As illustrated in the code above, I used map to get it to work but if there is a way to use a slice I'd like to learn how to do it.

Aside: If this is possible, though, it immediately implies one could slice across both directions at once:

# yikes!! print join( ' ', @hoh{@keys}{@keys} ), "\n"; # a1 a3 c1 c3 ??


Update: clarified the main question

In reply to Slicing multilevel hashes by bobf

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.