<?php
//recursive solution

//test array
$nested_array = [[1,2,[3]],4,[5],[[[6,[7=>[7,8,9,10]]]]]];

/*-----------------------------------------
function call and return result to an array
------------------------------------------*/
$index_count = 1;
$flatered_array = array();
$flatered_array = flat_array($nested_array, $index_count);

/*-----------------------------------------
Print Result
-----------------------------------------*/
echo "<pre>";
print_r($flatered_array);


/*-----------------------------------------
function to flaten an array 
-----------------------------------------*/
function flat_array($nested_array, & $index_count, & $flatered_array) {

  foreach($nested_array AS $key=>$val) {
      if(is_array($val)) {
        flat_array($val, $index_count, $flatered_array);
      }
      else {
        $flatered_array[$index_count] = $val;
        ++$index_count;
      }      
  }

return $flatered_array;
}
?>

/**
 * For merging values of a multidimensional array into one 
 *
 * $array = [
 *     0 => [
 *         0 => 'a1',
 *         1 => 'b1',
 *         2 => 'c1',
 *         3 => 'd1'
 *     ],
 *     1 => [
 *         0 => 'a2',
 *         1 => 'b2',
 *         2 => 'c2',
 *     ]
 * ];
 *
 * becomes : 
 *
 * $array = [
 *     0 => 'a1',
 *     1 => 'b1',
 *     2 => 'c1',
 *     3 => 'd1',
 *     4 => 'a2',
 *     5 => 'b2',
 *     6 => 'c2',
 *     
 * ]
 */
array_reduce
(
    $multiArray
    , function ($lastItem, $currentItem) {
        $lastItem = $lastItem ?: array();
        return array_merge($lastItem, array_values($currentItem));
    }
);

依据片段

如果你想保住你的钥匙，那就是解决办法。

function flatten(array $array) {
    $return = array();
    array_walk_recursive($array, function($value, $key) use (&$return) { $return[$key] = $value; });
    return $return;
}

不幸的是，它只输出最后的嵌套数组，没有中间键。对于下面的例子:

$array = array(
    'sweet' => array(
        'a' => 'apple',
        'b' => 'banana'),
    'sour' => 'lemon'); 
print_r(flatten($fruits));

输出是:

Array
(
    [a] => apple
    [b] => banana
    [sour] => lemon
)

如果你有一个对象数组，想用一个节点把它压平，只需要使用这个函数:

function objectArray_flatten($array,$childField) {
    $result = array();
    foreach ($array as $node)
    {
        $result[] = $node;
        if(isset($node->$childField))
        {
            $result = array_merge(
                $result, 
                objectArray_flatten($node->$childField,$childField)
            );
            unset($node->$childField);
        }

    }
    return $result;
}

<?php
//recursive solution

//test array
$nested_array = [[1,2,[3]],4,[5],[[[6,[7=>[7,8,9,10]]]]]];

/*-----------------------------------------
function call and return result to an array
------------------------------------------*/
$index_count = 1;
$flatered_array = array();
$flatered_array = flat_array($nested_array, $index_count);

/*-----------------------------------------
Print Result
-----------------------------------------*/
echo "<pre>";
print_r($flatered_array);


/*-----------------------------------------
function to flaten an array 
-----------------------------------------*/
function flat_array($nested_array, & $index_count, & $flatered_array) {

  foreach($nested_array AS $key=>$val) {
      if(is_array($val)) {
        flat_array($val, $index_count, $flatered_array);
      }
      else {
        $flatered_array[$index_count] = $val;
        ++$index_count;
      }      
  }

return $flatered_array;
}
?>

诀窍是通过引用传递源数组和目标数组。

function flatten_array(&$arr, &$dst) {
    if(!isset($dst) || !is_array($dst)) {
        $dst = array();
    }
    if(!is_array($arr)) {
        $dst[] = $arr;
    } else {
        foreach($arr as &$subject) {
            flatten_array($subject, $dst);
        }
    }
}

$recursive = array('1', array('2','3',array('4',array('5','6')),'7',array(array(array('8'),'9'),'10')));
echo "Recursive: \r\n";
print_r($recursive);
$flat = null;
flatten_array($recursive, $flat);

echo "Flat: \r\n";
print_r($flat);

// If you change line 3 to $dst[] = &$arr; , you won't waste memory,
// since all you're doing is copying references, and imploding the array 
// into a string will be both memory efficient and fast:)

echo "String:\r\n";
echo implode(',',$flat);