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Re: DBI's selectall_hashref and nested foreach loops

by anonymized user 468275 (Curate)
on Jul 06, 2005 at 11:14 UTC ( #472759=note: print w/replies, xml ) Need Help??


in reply to DBI's selectall_hashref and nested foreach loops

To avoid having one foreach per level in the hash, I would write a recursive hash traversal subroutine as in this (tested) example, which uses a single foreach in a subroutine that calls itself when it finds a hash reference instead of a value:

Update 1: the point of all this is not how many times foreach is actually executed but to avoid having to code differently for different nesting levels of the hash.

Update 2: modified to show how to make the actual processing of the hash flexible. The assignment into a flat array is just to demonstrate that all the values and none of the keys of the hash were covered. A slight change can make it do something else at each node.

Update 3: where the code examines ref($val), it could also be adapted to process arrays within hashes, by creating an extra branch for where ref($val) eq 'ARRAY'.

#!/usr/bin/perl use strict; use Data::Dumper; my %h = (); # stick in some data at varying depths $h{ 1}{ 2}{ 3} = 123; $h{1}{3} = 13; $h{2} = 2; # this array will collect the values my @flat = (); hashTraverse( \%h, \@flat ); print Dumper( \@flat ); sub hashTraverse { my ( $href, $aref ) = ( shift(), shift() ); foreach my $key ( sort keys %$href ) { # this simple example sorts + the tree left-right my $val = $href -> { $key }; if ( ref( $val ) eq 'HASH' ) { hashTraverse( $href -> { $key }, $aref ) } else { push @$aref, $val; # or instead whatever else should be done to or with the h +ash node } } }

Output:

$VAR1 = [ 123, 13, 2 ];

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