Generate multi dimensional array from list string

Question

I'd like to generate a multi-dimensional array in PHP from the following -

- Item 1
-- Item 1.1
-- Item 1.2
--- Item 1.2.1
--- Item 1.2.2
---- Item 1.2.2.1
- Item 2
- Item 3
- Item 4
-- Item 4.1
-- Item 4.2

My eventual aim is to convert this string into an unordered list.

I'd imagine the best way to do this would be to create a recursive function. On a good day I'm sure I could work this out but I'm having a bit of a mind blank!

The array structure should be something like the below dump -

array(6) {
  [0]=>
  string(6) "Item 1"
  [1]=>
  array(3) {
    [0]=>
    string(8) "Item 1.1"
    [1]=>
    string(8) "Item 1.2"
    [2]=>
    array(3) {
      [0]=>
      string(10) "Item 1.2.1"
      [1]=>
      string(10) "Item 1.2.2"
      [2]=>
      array(1) {
        [0]=>
        string(12) "Item 1.2.2.1"
      }
    }
  }
  [2]=>
  string(6) "Item 2"
  [3]=>
  string(6) "Item 3"
  [4]=>
  string(6) "Item 4"
  [5]=>
  array(2) {
    [0]=>
    string(8) "Item 4.1"
    [1]=>
    string(8) "Item 4.2"
  }
}

Hope you can help.

google.com/… // most of the results seem to be for PHP, but since you did not even mention or tag a specific language, that’ll have to do then I guess. — C3roe
– C3roe, Commented Feb 14, 2017 at 12:28
@CBroe thanks for the Google link. It's PHP - sorry I forgot to include that so have added it now. This is a little more complex than your standard string recursion — Chris
– Chris, Commented Feb 14, 2017 at 12:30
From above comments, can you give a hint how the array should look like? — user2284357
– user2284357, Commented Feb 14, 2017 at 12:37
You don't need recursion if the text is always well formed. Just count the dashes on each line, and use that to determine when to output <ul> and </ul> tags. I'll write an answer when a get a moment. — Guillermo Phillips
– Guillermo Phillips, Commented Feb 14, 2017 at 12:40
@NirjharLo I've updated my question to include intended output. — Chris
– Chris, Commented Feb 14, 2017 at 13:01

Guillermo Phillips · Accepted Answer · 2017-02-14 14:58:19Z

2

The following will convert straight into HTML without recursion:

$text = array();
$text[] = '- Item 1';
$text[] = '-- Item 1.1';
$text[] = '-- Item 1.2';
$text[] = '--- Item 1.2.1';
$text[] = '--- Item 1.2.2';
$text[] = '---- Item 1.2.2.1';
$text[] = '- Item 2';
$text[] = '- Item 3';
$text[] = '- Item 4';
$text[] = '-- Item 4.1';
$text[] = '-- Item 4.2';

$previous_dash_count = 0; // topmost parent
foreach ($text as $line) {
    if (preg_match('/(^\-+)(.*)/', $line, $matches, PREG_OFFSET_CAPTURE)===1) {
        $dash_count = strlen($matches[1][0]);
        $title = $matches[2][0];

        if ($dash_count == $previous_dash_count) {
            echo "<li>$title</li>\n";
        } elseif ($dash_count > $previous_dash_count) {
            echo str_repeat("<ul>\n", $dash_count - $previous_dash_count);
            echo "<li>$title</li>\n";
        } else {
            echo str_repeat("</ul>\n",$previous_dash_count-$dash_count+1);
            echo "<ul>\n";
            echo "<li>$title</li>\n";
        }

        $previous_dash_count = $dash_count;
    }
}
echo str_repeat("</ul>\n",$previous_dash_count);

I make several assumptions. That the input text always behaves well and doesn't contain randomness. Also I don't assume UTF-8 text, but you're safe with dashes.

Here is the array version in all its gory glory:

$stack = array();
$previous_dash_count = 0;
$parent_node = array();
foreach ($text as $line) {
    if (preg_match('/(^\-+)(.*)/', $line, $matches, PREG_OFFSET_CAPTURE)===1) {
        $dash_count = strlen($matches[1][0]);
        $title = $matches[2][0];

        if ($dash_count == $previous_dash_count) {
            $parent_node[] = $title;
        } elseif ($dash_count > $previous_dash_count) {
            for ($push_count = $previous_dash_count; $push_count<$dash_count; $push_count++) {
                array_push($stack, $parent_node); // remember node
                $new_child = array();
                $new_child[] = $title;
                $parent_node[] = $new_child;
                $parent_node = $new_child;
            }
        } else {
            for ($pop_count = $previous_dash_count; $pop_count >$dash_count; $pop_count--) {
                $old_child = $parent_node;
                $parent_node = array_pop($stack);
                $parent_node[] = $old_child;
            }
            $parent_node[] = $title;
        }

        $previous_dash_count = $dash_count;
    }
}
for ($pop_count = $previous_dash_count; $pop_count > 0; $pop_count--) {
    $old_child = $parent_node;
    $parent_node = array_pop($stack);
    $parent_node[] = $old_child;
}

print_r($parent_node);

We keep a stack of array nodes, so we have a link between a child and its parent. Note the structure of this code is identical to that for the straight HTML version.

edited Feb 14, 2017 at 14:58

answered Feb 14, 2017 at 13:11

Guillermo Phillips

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3 Comments

Chris Over a year ago

Thanks - I had to go for this kind of method in the end as it was the easiest. Slightly different technique but your answer is right nonetheless. Cheers!

Chris Over a year ago

Awesome on the array version too, thank you so much! Cudos :)

Chris Over a year ago

That's it - I had already given it a crack but you know those days when you're just really struggling to see the solution?!...

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