Creating a recursive category tree function

Question

I have a database with a bunch of categories, some are children:

What I'm trying to output is something like this:

<ul>
    <li>Parent
        <ul>
            <li>Child</li>
        </ul>
    </li>
    <li>Parent with no Children</li>
</ul>

I'm trying to build a recursive tree script in PHP, but I'm stuck. Here's what I have so far. I'm stuck on what to do between the else: and endif; in the foreach. (And I'm using that syntax just for easier reading here.) Any suggestions?

echo $this->categories->makeTree(0, $this->db->get('categories')->result_array());

public static function makeTree($parent, $array)
{
  if (!is_array($array)) return '';

  $output = '<ul>';

  foreach($array as $key => $value):
    if ($value['parent'] == $parent):
        $output .= '<li>';

        if ($value['parent'] == NULL):
            $output .= $value['name'];
        else:

        endif;
    endif;

    $output .= '</li>';
  endforeach;

  $output .= '</ul>';
  return $output;
}

EDIT 1

I was able to get this working, although I have a database call in a foreach loop, which probably isn't the best idea:

public function makeTree($parent, $array)
{
  if (!is_array($array)) return FALSE;

  $output = '<ul>';

  foreach($array as $key => $value):
    if ($value['parent'] == $parent):
        $output .= '<li>';

        if ($value['parent'] == NULL):
            $output .= $value['name'];

            $subcategories = ci()->db->get_where('categories', array('parent' => $value['id']));

            if ($subcategories->num_rows() > 0):
                $output .= $this->makeTree($value['id'], $subcategories->result_array());
            endif;
        else:
            $output .= $value['name'];
            $output .= '</li>';
        endif;
    endif;

  endforeach;

  $output .= '</ul>';
  return $output;
}

EDIT 2

Here is my final solution, reusing the array instead of doing a DB query:

public function makeTree($parent, $array)
{
  if (!is_array($array) OR empty($array)) return FALSE;

  $output = '<ul>';

  foreach($array as $key => $value):
    if ($value['parent'] == $parent):
        $output .= '<li>';

        if ($value['parent'] == NULL):
            $output .= $value['name'];

            $matches = array();

            foreach($array as $subkey => $subvalue):
                if ($subvalue['parent'] == $value['id']):
                    $matches[$subkey] = $subvalue;
                endif;
            endforeach;

            $output .= $this->makeTree($value['id'], $matches);

        else:
            $output .= $value['name'];
            $output .= '</li>';
        endif;
    endif;

  endforeach;

  $output .= '</ul>';

  return $output;
}

It is currently traversing 2 levels. Can we traverse it up to n level? — Iqbal Malik
– Iqbal Malik, Commented Dec 1, 2015 at 11:34

Community · Accepted Answer · 2017-05-23 12:30:20Z

10

Though this seems answered, have a look here. With the shown function you can convert your flat data to nested data with only one iteration. Creating an ul-list from that nested data is then very easy. For example:

function nested2ul($data) {
  $result = array();

  if (sizeof($data) > 0) {
    $result[] = '<ul>';
    foreach ($data as $entry) {
      $result[] = sprintf(
        '<li>%s %s</li>',
        $entry['name'],
        nested2ul($entry['children'])
      );
    }
    $result[] = '</ul>';
  }

  return implode($result);
}

echo nested2ul(array(flat2nested( $yourFlatData ));

The good thing about this approach is that you don't have to re-iterate again and again over the input data just to find the child-elements.

edited May 23, 2017 at 12:30

CommunityBot

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answered Sep 6, 2012 at 8:02

Yoshi

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2 Comments

dallen Over a year ago

I like that, but I keep getting "Undefined offset: 0" at return $m[$r][0]; in the makeRecursive function. That function is expecting data like array(array('id' => 5273, 'parent' => 0)) whereas my array is Array([0] => Array([id] => 1, [parent] => 0)). Any suggestion on how I can fix this?

Yoshi Over a year ago

@dallen the two snippets you posted are actually the same. I guess the problem is that your root parent value is an empty string. Whereas the helper function uses 0 (see the $r parameter). An empty string as an array key is a bit problematic, so if you could change that in your input data, I think the rest should work.

dallen · Accepted Answer · 2012-09-05 19:47:10Z

Here is my final solution, reusing the array instead of doing a DB query. If you do have a better solution, please post!

public function makeTree($parent, $array)
{
  if (!is_array($array) OR empty($array)) return FALSE;

  $output = '<ul>';

  foreach($array as $key => $value):
    if ($value['parent'] == $parent):
        $output .= '<li>';

        if ($value['parent'] == NULL):
            $output .= $value['name'];

            $matches = array();

            foreach($array as $subkey => $subvalue):
                if ($subvalue['parent'] == $value['id']):
                    $matches[$subkey] = $subvalue;
                endif;
            endforeach;

            $output .= $this->makeTree($value['id'], $matches);

        else:
            $output .= $value['name'];
            $output .= '</li>';
        endif;
    endif;

  endforeach;

  $output .= '</ul>';

  return $output;
}

Pluda · Accepted Answer · 2012-09-05 17:15:25Z

1

I usualy use something like this, please note

1st this piece of code is using deprecated mysql_*

2nd you should have one database field named level, if NULL it is the main category, if it has a number, it is a subcategory of the category with that number as id

function getFamilies($level = 0) {
    $level++;
    $sql = "SELECT id from families WHERE level IS NULL";
    if (mysql_num_rows($result) > 0) {
        echo "<ul>";
            while($row = mysql_fetch_assoc($result)) {
                echo "<li>".$row['id'];
                    getSubFamilies($level, $row['id']);
                echo "</li>";
            }
        echo "</ul>";
    }
}

function getSubFamilies($level, $id) {
    $level++;
    $sqlSubFamilies = "SELECT id  FROM families WHERE level = ".$id."";
    $resultSubFamilies = mysql_query($sqlSubFamilies);
    if (mysql_num_rows($resultSubFamilies) > 0) {
        echo = "<ul>";
            while($rowSubFamilies = mysql_fetch_assoc($resultSubFamilies)) {
                echo "<li>".$rowSubFamilies['id'];
                    getSubFamilies($level, $rowSubFamilies['id']);
                echo "</li>";
            }
        echo "</ul>";
    }
}

getFamilies($level = 0);

edited Sep 5, 2012 at 17:15

answered Sep 5, 2012 at 17:09

Pluda

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1 Comment

Pluda Over a year ago

in your case, level is parent, so "select id, name from categories where parent is null"

sw04 · Accepted Answer · 2012-09-05 16:55:38Z

0

try this:

$cats = $this->db->get('categories')->result_array();

echo $this->categories->makeTree(0, $cats);

public static function makeTree($parent, $array)
{
  if (!is_array($array)) return '';

  $output = '<ul>';

  foreach($array as $key => $value):
    if ($value['parent'] == $parent):
        $output .= '<li>';

        if ($value['parent'] == NULL):
            $output .= $value['name'];
        else:

        endif;
    endif;

    $output .= '</li>';

    $output .= $this->categories->makeTree($value['parent'], $cats);

  endforeach;

  $output .= '</ul>';
  return $output;
}

answered Sep 5, 2012 at 16:55

sw04

1

Comments

Martin Zvarík · Accepted Answer · 2022-10-06 21:39:42Z

-2

I think this method using anonymous function is very simple.

//--------------------------- PRINT NESTED CATEGORIES
$cats_childs = array();

$q = $db->query("SELECT id, parent, name FROM categories");

while ($r = $db->row($q))
{
    $cats_childs[$r['parent']][$r['id']] = $r;
}

$nested2ul = function($items, $childs = null) use (&$nested2ul) {
    if (!empty($items)) {
        echo '<ul>';
        foreach ($items as $r) {
            echo '<li>';
            echo $r['name'];
            $nested2ul($childs[$r['id']]);
            echo '</li>';
        }
        echo '</ul>';
    }
};

echo $nested2ul($cats_childs[0], $cats_childs);

edited Oct 6, 2022 at 21:39

answered Sep 7, 2017 at 0:19

Martin Zvarík

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