How to “flatten” a multi-dimensional array to simple one in PHP?

Question

It\'s probably beginner question but I\'m going through documentation for longer time already and I can\'t find any solution. I thought I could use implode for each dimensio

Answer 1

A new approach based on the previous example function submited by chaos, which fixes the bug of overwritting string keys in multiarrays:

# Flatten a multidimensional array to one dimension, optionally preserving keys.
# $array - the array to flatten
# $preserve_keys - 0 (default) to not preserve keys, 1 to preserve string keys only, 2 to preserve all keys
# $out - internal use argument for recursion

function flatten_array($array, $preserve_keys = 2, &$out = array(), &$last_subarray_found) 
{
        foreach($array as $key => $child)
        {
            if(is_array($child))
            {
                $last_subarray_found = $key;
                $out = flatten_array($child, $preserve_keys, $out, $last_subarray_found);
            }
            elseif($preserve_keys + is_string($key) > 1)
            {
                if ($last_subarray_found)
                {
                    $sfinal_key_value = $last_subarray_found . "_" . $key;
                }
                else
                {
                    $sfinal_key_value = $key;
                }
                $out[$sfinal_key_value] = $child;
            }
            else
            {
                $out[] = $child;
            }
        }

        return $out;
}

Example:
$newarraytest = array();
$last_subarray_found = "";
$this->flatten_array($array, 2, $newarraytest, $last_subarray_found);

Answer 2

Another method from PHP's user comments (simplified) and here:

function array_flatten_recursive($array) { 
   if (!$array) return false;
   $flat = array();
   $RII = new RecursiveIteratorIterator(new RecursiveArrayIterator($array));
   foreach ($RII as $value) $flat[] = $value;
   return $flat;
}

The big benefit of this method is that it tracks the depth of the recursion, should you need that while flattening.
This will output:

$array = array( 
    'A' => array('B' => array( 1, 2, 3)), 
    'C' => array(4, 5) 
); 
print_r(array_flatten_recursive($array)); 

#Returns: 
Array ( 
    [0] => 1 
    [1] => 2 
    [2] => 3 
    [3] => 4 
    [4] => 5 
)

Answer 3

With PHP 7, you can use generators and generator delegation (yield from) to flatten an array:

function array_flatten_iterator (array $array) {
    foreach ($array as $value) {
        if (is_array($value)) {
            yield from array_flatten_iterator($value);
        } else {
            yield $value;
        }
    }
}

function array_flatten (array $array) {
    return iterator_to_array(array_flatten_iterator($array), false);
}

Example:

$array = [
    1,
    2,
    [
        3,
        4,
        5,
        [
            6,
            7
        ],
        8,
        9,
    ],
    10,
    11,
];    

var_dump(array_flatten($array));

http://3v4l.org/RU30W

Answer 4

Using higher-order functions (note: I'm using inline anonymous functions, which appeared in PHP 5.3):

function array_flatten($array) {
    return array_reduce(
        $array,
        function($prev, $element) {
            if (!is_array($element))
                $prev[] = $element;
            else
                $prev = array_merge($prev, array_flatten($element));
            return $prev;
        },
        array()
    );
}

Answer 5

Someone might find this useful, I had a problem flattening array at some dimension, I would call it last dimension so for example, if I have array like:

array (
  'germany' => 
  array (
    'cars' => 
    array (
      'bmw' => 
      array (
        0 => 'm4',
        1 => 'x3',
        2 => 'x8',
      ),
    ),
  ),
  'france' => 
  array (
    'cars' => 
    array (
      'peugeot' => 
      array (
        0 => '206',
        1 => '3008',
        2 => '5008',
      ),
    ),
  ),
)

Or:

array (
  'earth' => 
  array (
    'germany' => 
    array (
      'cars' => 
      array (
        'bmw' => 
        array (
          0 => 'm4',
          1 => 'x3',
          2 => 'x8',
        ),
      ),
    ),
  ),
  'mars' => 
  array (
    'france' => 
    array (
      'cars' => 
      array (
        'peugeot' => 
        array (
          0 => '206',
          1 => '3008',
          2 => '5008',
        ),
      ),
    ),
  ),
)

For both of these arrays when I call method below I get result:

array (
  0 => 
  array (
    0 => 'm4',
    1 => 'x3',
    2 => 'x8',
  ),
  1 => 
  array (
    0 => '206',
    1 => '3008',
    2 => '5008',
  ),
)

So I am flattening to last array dimension which should stay the same, method below could be refactored to actually stop at any kind of level:

function flattenAggregatedArray($aggregatedArray) {
    $final = $lvls = [];
    $counter = 1;
    $lvls[$counter] = $aggregatedArray;


    $elem = current($aggregatedArray);

    while ($elem){
        while(is_array($elem)){
            $counter++;
            $lvls[$counter] = $elem;
            $elem =  current($elem);
        }

        $final[] = $lvls[$counter];
        $elem = next($lvls[--$counter]);
        while ( $elem  == null){
            if (isset($lvls[$counter-1])){
                $elem = next($lvls[--$counter]);
            }
            else{
                return $final;
            }
        }
    }
}

Answer 6

If you're interested in just the values for one particular key, you might find this approach useful:

function valuelist($array, $array_column) {
    $return = array();
    foreach($array AS $row){
        $return[]=$row[$array_column];
    };
    return $return;
};

Example:

Given $get_role_action=

array(3) {
  [0]=>
  array(2) {
    ["ACTION_CD"]=>
    string(12) "ADD_DOCUMENT"
    ["ACTION_REASON"]=>
    NULL
  }
  [1]=>
  array(2) {
    ["ACTION_CD"]=>
    string(13) "LINK_DOCUMENT"
    ["ACTION_REASON"]=>
    NULL
  }
  [2]=>
  array(2) {
    ["ACTION_CD"]=>
    string(15) "UNLINK_DOCUMENT"
    ["ACTION_REASON"]=>
    NULL
  }
}

than $variables['role_action_list']=valuelist($get_role_action, 'ACTION_CD'); would result in:

$variables["role_action_list"]=>
  array(3) {
    [0]=>
    string(12) "ADD_DOCUMENT"
    [1]=>
    string(13) "LINK_DOCUMENT"
    [2]=>
    string(15) "UNLINK_DOCUMENT"
  }

From there you can perform value look-ups like so:

if( in_array('ADD_DOCUMENT', $variables['role_action_list']) ){
    //do something
};