Question

Have an array of hashes,

my @arr = get_from_somewhere();

the @arr contents (for example) is:

@arr = (
  { id => "id2",    requires => 'someid', text => "another text2" },
  { id => "xid4",   requires => 'id2',    text => "text44" },
  { id => "someid", requires => undef,    text => "some text" },
  { id => "id2",    requires => 'someid', text => "another text2" },
  { id => "aid",    requires => undef,    text => "alone text" },
  { id => "id2",    requires => 'someid', text => "another text2" },
  { id => "xid3",   requires => 'id2',    text => "text33" },
);

need something like:

my $texts = join("\n",  get_ordered_texts(@arr) );

soo need write a sub what return the array of texts from the hashes, – in the dependent order, so from the above example need to get:

"some text",     #someid the id2 depends on it - so need be before id2
"another text2", #id2    the xid3 and xid4 depends on it - and it is depends on someid
"text44",        #xid4   the xid4 and xid3 can be in any order, because nothing depend on them
"text33",        #xid3   but need be bellow id2
"alone text",    #aid    nothing depends on aid and hasn't any dependencies, so this line can be anywhere

as you can see, in the @arr can be some duplicated “lines”, (“id2” in the above example), need output only once any id.

Not providing any code example yet, because havent any idea how to start. ;(
Exists some CPAN module what can be used to the solution?

Can anybody points me to the right direction?

Answer 1

Using Graph:

use Graph qw( );

my @recs = (
   { id => "id2",    requires => 'someid', text => "another text2" },
   { id => "xid4",   requires => 'id2',    text => "text44" },
   { id => "someid", requires => undef,    text => "some text" },
   { id => "id2",    requires => 'someid', text => "another text2" },
   { id => "aid",    requires => undef,    text => "alone text" },
   { id => "id2",    requires => 'someid', text => "another text2" },
   { id => "xid3",   requires => 'id2',    text => "text33" },
);

sub get_ordered_recs {
   my %recs;
   my $graph = Graph->new();
   for my $rec (@_) {
      my ($id, $requires) = @{$rec}{qw( id requires )};

      $graph->add_vertex($id);
      $graph->add_edge($requires, $id) if $requires;

      $recs{$id} = $rec;
   }

   return map $recs{$_}, $graph->topological_sort();
}

my @texts = map $_->{text}, get_ordered_recs(@recs);