You can use splice to extract regions out if the original array (i.e. if you don't want to copy to a new one)

Otherwise just slice and copy.

 $new[$i++] =  [ @old[$start..$end ] ]

edit

And for traversing use a recursive function which calls itself when an array-ref is read.

I thought about AoA, but that is not enought. For example:

[1,2,3,4,5,6,7,8,9]

should be converted to something like this:

[1,[2,3,4],5,[6,[7,8,9]]]

What is missing in this structure is the placeholder, which will have a group name... that's a new value in the list!

I guess that I could manage the first element in each list as the name of the placeholder, resulting something like this:

[A,1,[B,2,3,4],5,[C,6,[D,7,8,9]]]

BTW, while traversing, how could I recognize if current element is a scalar or another list to recurse?

> how could I recognize if current element is a scalar or another list to recurse?

with ref

> What is missing in this structure is theplaceholder, which will have a group name... 

No idea what you may mean...

update

Maybe

 [ {A => [1, {B => [2,3,4]} ,5, {C => [ 6, { D => [7,8,9] } ] } ]

? ? ?

(untested)

update

TIMTOWTDI

Instead of a one element hash you could use a 2 element array.

Or put the "placeholder" into the sub array as first element.

I personally prefer the hash solution for readability, but keep in mind that keys are stringified.

Cheers Rolf

_{(addicted to the Perl Programming Language and ☆☆☆☆ :)}

Using splice to replace a subset of the top level array with an anonymous array holding the values replaced is fairly easy:

@sorted = 0 .. 9;;

splice @sorted, 1, 8, [ @sorted[ 1 .. 8 ] ];;

pp @sorted;;
(0, [1, 2, 3, 4, 5, 6, 7, 8], 9)
[download]

However, if you need to perform that same operation on one of the nested anonymous arrays, it gets somewhat more complicated:

splice @{ $sorted[1] }, 1, 6, [ @{ $sorted[ 1] }[ 1 .. 6 ] ];;

pp @sorted;;
(0, [1, [2, 3, 4, 5, 6, 7], 8], 9)
[download]

And if you need to go deeper still, it starts to get quite unweildy:

splice @{ $sorted[1][1] }, 1, 4, [ @{ $sorted[1][1] }[ 1 .. 4 ] ];;

pp @sorted;;
(0, [1, [2, [3, 4, 5, 6], 7], 8], 9)
[download]

That makes no sense as a solution to the OP's question.

The nodes in the original list are unique, and actually are the keys of some hashes, and the order in the list is based on one of them. The new ones (branches) are labels that group some old nodes based on values from other hash, and it's name will not duplicate any existing key. Being the first element of any nested list is enougth to know the type of it.

I think I'll start with about a thousand nodes in a list, and I don't know how "tall" the resulting tree will be. It'll depend on some tunning of the parameters.

With the inserted placeholder in the first position of every array as a grouping item, the traverse subroutune looks like this:

my @xx = ['A',1,['B',2,3,4],5,['C',6,['D',7,8,9]]];

traverse("", @xx);

sub traverse {
  my $d = $_[0] . "/" . $_[1][0];
  for my $i (1 .. @{$_[1]}-1) {
    if (ref $_[1][$i] eq 'ARRAY') {
      traverse($d, $_[1][$i]);
    } else {
      print $d . "/" . $_[1][$i] . "\n";
    }
  }
}
[download]

The result is:

/A/1
/A/B/2
/A/B/3
/A/B/4
/A/5
/A/C/6
/A/C/D/7
/A/C/D/8
/A/C/D/9
[download]

I tried to manage the route of groups and subgroups with another array, but got this message when trying to add the first items from the second array to the first one:

Can't use string ("A") as an ARRAY ref while "strict refs" in use at t
+est.pl line 6
[download]

I couldnīt get rid of it. I also tried passing the arguments by reference, but I got many other error mesages on every change I did.

your mom is a special tree