mysql - How to create nested category list from category-strings in PHP

Answer

Solution:

Just construct your tree using the categories as the node's key. For example :

$categoryLines = array(
    "female / dresses / long",
    "female / dresses / short",
    "female / shoes",
    "male / shoes / sneakers / skate"
);

function buildCategoryTree($categoryLines, $separator) {
    $catTree = array();
    foreach ($categoryLines as $catLine) {
       $path = explode($separator, $catLine);
       $node = & $catTree;
       foreach ($path as $cat) {
           $cat = trim($cat);
           if (!isset($node[$cat])) {
               $node[$cat] = array();
           }
           $node = & $node[$cat];
       }
    }
    return $catTree;
}

function displayCategoryTree($categoryTree, $indent = '') {
    foreach ($categoryTree as $node => $children) {
        echo $indent . $node . "\n";
        displayCategoryTree($children, $indent . '|- ');
    }
}

$categoryTree = buildCategoryTree($categoryLines, '/');
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Now,var_export($categoryTree) will output :

array (
  'female' => array (
    'dresses' => array (
      'long' => array (),
      'short' => array (),
    ),
    'shoes' => array (),
  ),
  'male' => array (
    'shoes' => array (
      'sneakers' => array (
        'skate' => array (),
      ),
    ),
  ),
)
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anddisplayCategoryTree($categoryTree) will output :

female
|- dresses
|- |- long
|- |- short
|- shoes
male
|- shoes
|- |- sneakers
|- |- |- skate
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** Edit **

To get the HTML representation of the tree :

function displayHtmlCategoryTree($categoryTree, $id = null, $pathSeparator = '/', $parents = '') {
    if (empty($categoryTree)) return '';

    $str = '<ul' . (!empty($id) ? ' id="'.$id.'"' : '') . '>';
    foreach ($categoryTree as $node => $children) {
        $currentPath = $parents . (empty($parents) ? '' : $pathSeparator) . $node;
        $str .= '<li title="' . $currentPath . '">' . $node . 
                displayHtmlCategoryTree($children, null, $pathSeparator, $currentPath) . 
                '</li>';
    }
    $str .= '</ul>';
    return $str;
}

echo displayHtmlCategoryTree($categoryTree, "test", ' / ');
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and will output :

<ul id="test"><li title="female">female<ul><li title="female / dresses">dresses<ul><li title="female / dresses / long">long</li><li title="female / dresses / short">short</li></ul></li><li title="female / shoes">shoes</li></ul></li><li title="male">male<ul><li title="male / shoes">shoes<ul><li title="male / shoes / sneakers">sneakers<ul><li title="male / shoes / sneakers / skate">skate</li></ul></li></ul></li></ul></li></ul>
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Answer

Solution:

As others mentioned in comments, you'd better to usenested tree sets for this kind of categorization, but since you asked you don't want to change the scheme of your category system and IF and only IF you're not concerned about your run-time overload, you can use this code that I wrote.

For populating an array of categories:

<?php
  $rows = array(
    "female/dresses/long",
    "female/dresses/short",
    "female/dresses/short/1",
    "female/dresses/short/2",
    "female/dresses/short/2/1",
    "female/shoes",
    "male/shoes/sneakers/skate"
  );

  $categories = array();

  function populate()
  {
    global $rows;
    global $categories;

    foreach($rows as $row)
    {
      $category_array = explode(" / ", $row);

      $categories = place($categories, $category_array);
    }
  }

  function place($categories, $category, $counter = 0)
  {
    if($counter < count($category))
    {
      if(!isset($categories[$category[$counter]]))
      {
        $categories[$category[$counter]] = array();
      }
      else if($counter == count($category) - 1)
      {
        $categories[$category[$counter]][] = $category[$counter];
      }

      // Recurse
      $categories[$category[$counter]] = place($categories[$category[$counter]], $category, $counter + 1);
    }

    return $categories;
  }

  // Populate categories
  populate();
?>
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You can replace myforeach on$rows with your fetchwhile loop.

For displaying of categories:

<?php
  function display($items)
  {
    foreach($items as $k => $v)
    {
      echo "<li>" . $k;

      if(is_array($v))
      {
        echo "<ul>";

        display($v);

        echo "</ul>";
      }

      echo "</li>";
    }
  }
?>

<!DOCTYPE HTML>

<html>

<head>
  <title>Categories</title>
</head>

<body>
  <ul>
  <?php
    // Display categories
    display($categories);
  ?>
  </ul>
</body>

</html>
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Current demonstration:

female
    dresses
        long
        short
            1
            2
                1
    shoes

male
    shoes
        sneakers
            skate
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