Question

I’m having a strange problem while building arrays. I start off with an array that looks like this:

Array (
       [0] => Array (
                      [tag_id] => 19
                      [tag_translation_id] => 12
                      [fk_language_id] => 1
                      [fk_tag_id] => 19
                      [tag_name] => test
                    )
       [1] => Array (
                      [tag_id] => 20
                      [tag_translation_id] => 14
                      [fk_language_id] => 1
                      [fk_tag_id] => 20
                      [tag_name] => testa
                    )
       [2] => Array (
                      [tag_id] => 20
                      [tag_translation_id] => 15
                      [fk_language_id] => 3
                      [fk_tag_id] => 20
                      [tag_name] => fdfda
                    )
       )

What I want to do is merge each result with the same tag_id into a single array. This works:

    $tags = array();
    foreach($results->as_array() as $key=>$result)
    {
        if(!in_array($result['tag_id'], $tags))
        {
            $tags[$result['tag_id']] = array();
        }   
    }

    foreach($results->as_array() as $result)
    {
        array_push($tags[$result['tag_id']], array($result['fk_language_id'] , $result['tag_name']));   
    }

Here is the intended result:

Array ( 
  [19] => Array ( 
       [0] => Array ( 
               [0] => 1 
               [1] => test 
           ) 
       ) 
  [20] => Array ( 
       [0] => Array ( 
               [0] => 1 
               [1] => testa 
           ) 
       [1] => Array (  
               [0] => 3 
               [1] => fdfda 
           ) 
       ) 
) 

However, I’ve got two loops here, and I know this isn’t ideal. Why do THESE not work??

    $tags = array();
    foreach($results->as_array() as $key=>$result)
    {
        $tags[$result['tag_id']] .= array($result['fk_language_id'] , $result['tag_name']);
    }

With this example I get two empty arrays…

Array ( [19] => Array [20] => ArrayArray ) 

Or even…

    $tags = array();
    foreach($results->as_array() as $key=>$result)
    {
        if(!in_array($result['tag_id'], $tags))
        {
            $tags[$result['tag_id']] = array();
        }
        array_push($tags[$result['tag_id']], array($result['fk_language_id'] , $result['tag_name']));
    }

Which for some reason overwrites the first value of the second array with the second value of the second array.

Array ( 
  [19] => Array ( 
       [0] => Array ( 
               [0] => 1 
               [1] => test 
           ) 
       ) 
  [20] => Array ( 
      [0] => Array ( 
               [0] => 3 
               [1] => fdfda 
           ) 
       ) 
 ) 

What am I doing wrong in the second 2 examples?

Answer 1

To answer your question, your second method fails because you’re using the incorrect .= operator. Your third method fails because your !in_array check is always false (it checks whether the value is in the array, not whether the key is set) and overwrites the array each iteration. You only really need this (as mentioned by others, in pseudo-code):

$result = array();
foreach ($array as $values) {
    $result[$values['key']][] = array($values['foo'], $values['bar']);
}