Group 2d array data by 1 column and create subarrays in each group from other columns

Question

So I'm working on a website with Doctrine as ORM and I get the following array back as a result:

Array (
    [0] => Array (
        [c_cat_id] => 1
        [c_title] => Programas e projetos
        [p_menu] => PBA BR 163
        [p_page_id] => 1
    )
    [1] => Array (
        [c_cat_id] => 1
        [c_title] => Programas e projetos
        [p_menu] => Outros projetos
        [p_page_id] => 3
    )
)

Is it possible to transform this array (in PHP) to something like this:

Array (
    [0] => Array (
        [c_cat_id] => 1
        [c_title] => Programas e projetos
        [pages] => Array (
            [0] => Array (
                [p_page_id] => 1
                [p_menu] => PBA BR 163
            )
            [1] => Array (
                [p_page_id] => 3
                [p_menu] => Outros projetos
            )
        )
    )
)

@Samir: I would not change the code such that it makes sense. Formatting and so is fine but don't add stuff because of guess. If something is wrong, the OP has to correct it. — Felix Kling
– Felix Kling, Commented Apr 20, 2010 at 20:10

gnarf · Accepted Answer · 2010-04-20 20:14:44Z

Tested and working:

Code:

$original = array(
  array(
    "c_cat_id" => "1",
    "c_title" => "Programas e projetos",
    "p_menu" => "PBA BR 163",
    "p_page_id" => "1"),
  array(
    "c_cat_id" => "1",
    "c_title" => "Programas e projetos",
    "p_menu" => "Outros projetos",
    "p_page_id" => "3"),
  array(
    "c_cat_id" => "2",
    "c_title" => "Another Cat",
    "p_menu" => "Outros projetos",
    "p_page_id" => "4"),
);
$result = array();

foreach ($original as $row) {
  $cat = $row['c_cat_id'];
  if (!isset($result[$cat])) {
    $result[$row['c_cat_id']] = array(
      'c_cat_id'=>$row['c_cat_id'],
      'c_title'=>$row['c_title'],
      'pages'=>array(),
    );
  }
  unset($row['c_cat_id'],$row['c_title']);
  $result[$cat]['pages'][] = $row;
}

var_dump($result);

Result:

array(2) {
  [1]=>
  array(3) {
    ["c_cat_id"]=>
    string(1) "1"
    ["c_title"]=>
    string(20) "Programas e projetos"
    ["pages"]=>
    array(2) {
      [0]=>
      array(2) {
        ["p_menu"]=>
        string(10) "PBA BR 163"
        ["p_page_id"]=>
        string(1) "1"
      }
      [1]=>
      array(2) {
        ["p_menu"]=>
        string(15) "Outros projetos"
        ["p_page_id"]=>
        string(1) "3"
      }
    }
  }
  [2]=>
  array(3) {
    ["c_cat_id"]=>
    string(1) "2"
    ["c_title"]=>
    string(11) "Another Cat"
    ["pages"]=>
    array(1) {
      [0]=>
      array(2) {
        ["p_menu"]=>
        string(15) "Outros projetos"
        ["p_page_id"]=>
        string(1) "4"
      }
    }
  }
}

Fletcher Moore · Accepted Answer · 2010-04-20 20:17:48Z

It looks like you want to take an Array of pages and turn it into an array of categories with each containing an array of pages.

$inputArray = array(...); // whatever you have originally
$catArray = array();
foreach($inputArray as $page) {
  addToCatArray($page);
}

function addToCatArray($page) {
  $found = false;
  foreach($catArray as $cat) {
    if ($cat['c_cat_id'] == $page['c_cat_id'] {
      $newPage = array('p_page_id' => $page['p_page_id'], 'p_menu' => $page['p_menu']);
      $cat['pages'][] = $newPage;
      $found = true;
      break;
    }
  }
  if (!$found) { // create a new category
    $newCat = array('c_cat_id' => $page['c_cat_id'], 'c_title' => $page['c_title']);
    $newPage = array('p_page_id' => $page['p_page_id'], 'p_menu' => $page['p_menu']);
    $newCat['pages'] = array($newPage);
    $catArray[] = $newCat;
  }
}

Yeah sorry if I wasn't that clear but this is exactly what I want.

mickmackusa · Accepted Answer · 2024-09-12 21:22:59Z

As you iterate each row of the input array, split the data into two arrays -- the parent level data and the child level data. array_chunk() is concise and suitable for this asked question, but other scenarios may require different techniques.
Check if the grouping identifier has been encountered before. If not, create a new reference variable, fill it with the required array, then push it into the result array. If the identifier has been encountered already, just push the child data as a new subarray into the appropriate reference array.
Using references this way avoids the need to reindex the result array after looping

Code: (Demo)

$result = [];
foreach ($array as $row) {
    [$parent, $child] = array_chunk($row, 2, true);
    if (!isset($ref[$parent['c_cat_id']])) {
        $ref[$parent['c_cat_id']] = $parent + ['pages' => [$child]];
        $result[] =& $ref[$parent['c_cat_id']];
        continue;
    }
    $ref[$parent['c_cat_id']]['pages'][] = $child;
}

var_export($result);

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