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Re: Build tree data structure from DB (flat) data; function golf

by stvn (Monsignor)
on Aug 30, 2006 at 19:25 UTC ( #570458=note: print w/ replies, xml ) Need Help??


in reply to Build tree data structure from DB (flat) data; function golf

Well I didn't convert the foreach to a map, but I did remove some of your repeated code (closures++), and got rid of some checks and the a tiernary.

One note, though, this is a destructive function. When I tested the deeper case, it did not work because the original data structure ($old_data) is destroyed during the building of the tree. This is kind of a gotcha.

sub tree_data { my ( $old_data, $key_name, $next_group, @remaining_keys ) = @_; # guard against bad input and serve as recursion end case return $old_data unless defined $key_name; my @new_data; my $last_key = ''; # if this is initialized, you dont have to check + below my $build_box = []; # initalize this explicity (more self documentin +g) # encapsulate code into inner sub # fortunately for us, all variables # are closed over too :) my $push_new_data = sub { return unless $last_key; push @new_data, { $key_name => $last_key, $next_group => tree_data( $build_box, @remaining_keys ) }; # re-init this $build_box = []; }; foreach ( @{ $old_data } ) { if ( $last_key ne $_->{ $key_name } ) { $push_new_data->(); } $last_key = delete $_->{ $key_name }; push @{ $build_box }, $_; } $push_new_data->(); return \@new_data; }

Here is a complete test script which compares against the old one.

#!/usr/bin/perl use strict; use warnings; use Storable 'dclone'; use Data::Dumper; use Test::More no_plan => 1; sub orig_tree_data { my ( $old_data, $key_name, $next_group, @remaining_keys ) = @_; my ( @new_data, $last_key, $build_box ); foreach ( @{ $old_data } ) { if ( $last_key and ( $last_key ne $_->{ $key_name } ) ) { push @new_data, { $key_name => $last_key, $next_group => ( @remaining_keys ) ? tree_data( $build_box, @remaining_keys ) : $build_box, }; undef $build_box; } $last_key = delete $_->{ $key_name }; push @{ $build_box }, $_; } push @new_data, { $key_name => $last_key, $next_group => ( @remaining_keys ) ? tree_data( $build_box, @remaining_keys ) : $build_box, }; return \@new_data; } sub tree_data { my ( $old_data, $key_name, $next_group, @remaining_keys ) = @_; # guard against bad input and serve as recursion end case return $old_data unless defined $key_name; my @new_data; my $last_key = ''; # if this is initialized, you dont have to check + below my $build_box = []; # initalize this explicity (more self documentin +g) # encapsulate code into inner sub # fortunately for us, all variables # are closed over too :) my $push_new_data = sub { return unless $last_key; push @new_data, { $key_name => $last_key, $next_group => tree_data( $build_box, @remaining_keys ) }; # re-init this $build_box = []; }; foreach ( @{ $old_data } ) { if ( $last_key ne $_->{ $key_name } ) { $push_new_data->(); } $last_key = delete $_->{ $key_name }; push @{ $build_box }, $_; } $push_new_data->(); return \@new_data; } my $input = [ { 'team' => 'A-Team', 'employee' => 'Face', 'work_day' => '2006-08-28', 'other_data' => '123456789', }, { 'team' => 'A-Team', 'employee' => 'Murdock', 'work_day' => '2006-08-28', 'other_data' => '123456789', }, { 'team' => 'Military', 'employee' => 'Decker', 'work_day' => '2006-08-28', 'other_data' => '123456789', }, ]; my $input2 = dclone($input); my $input3 = dclone($input); my $input4 = dclone($input); is_deeply( tree_data( $input, 'team', 'employees' ), orig_tree_data( $input2, 'team', 'employees' ), '... both the same'); is_deeply( tree_data($input3, 'team', 'employees', 'employee', 'work_days'), orig_tree_data($input4, 'team', 'employees', 'employee', 'work_day +s'), '... both the same again');

-stvn


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Re^2: Build tree data structure from DB (flat) data; function golf
by gryphon (Abbot) on Aug 30, 2006 at 19:59 UTC

    Greetings stvn,

    This is awesome. Thanks! I need to reprogram my brain so I'll think to use closures more readily. Maybe I need to re-read HOP. You make a great point about this being a destructive function. I think it's easy to fix, though:

    $last_key = delete $_->{ $key_name }; push @{ $build_box }, $_;

    ...becomes...

    push @{ $build_box }, $_; $last_key = delete $build_box->[-1]{$key_name};

    UPDATE: I'm a crazy idiot. This doesn't do what I claim it should do. Bad programmer. No cookie. All I'm doing is moving the reference. I need to deep copy instead.

    gryphon
    Whitepages.com Development Manager (WDDC)
    code('Perl') || die;

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