使用递归。希望在看到它有多简单的时候，你对递归的恐惧会在你看到它有多简单的时候消失。

function flatten($array) {
    if (!is_array($array)) {
        // nothing to do if it's not an array
        return array($array);
    }

    $result = array();
    foreach ($array as $value) {
        // explode the sub-array, and add the parts
        $result = array_merge($result, flatten($value));
    }

    return $result;
}


$arr = array('foo', array('nobody', 'expects', array('another', 'level'), 'the', 'Spanish', 'Inquisition'), 'bar');
echo '<ul>';
foreach (flatten($arr) as $value) {
    echo '<li>', $value, '</li>';
}
echo '<ul>';

输出:

<ul><li>foo</li><li>nobody</li><li>expects</li><li>another</li><li>level</li><li>the</li><li>Spanish</li><li>Inquisition</li><li>bar</li><ul>

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);

对于php 5.2

function flatten(array $array) {
    $result = array();

    if (is_array($array)) {
        foreach ($array as $k => $v) {
            if (is_array($v)) {
                $result = array_merge($result, flatten($v));
            } else {
                $result[] = $v;
            }
        }
    }

    return $result;
}

我相信这是最干净的解决方案，不使用任何突变或不熟悉的类。

<?php

function flatten($array)
{
    return array_reduce($array, function($acc, $item){
        return array_merge($acc, is_array($item) ? flatten($item) : [$item]);
    }, []);
}


// usage
$array = [1, 2, [3, 4], [5, [6, 7]], 8, 9, 10];
print_r(flatten($array));

这个解是非递归的。注意，元素的顺序会有些混合。

function flatten($array) {
    $return = array();
    while(count($array)) {
        $value = array_shift($array);
        if(is_array($value))
            foreach($value as $sub)
                $array[] = $sub;
        else
            $return[] = $value;
    }
    return $return;
}

试试下面这个简单的函数:

function _flatten_array($arr) {
  while ($arr) {
    list($key, $value) = each($arr); 
    is_array($value) ? $arr = $value : $out[$key] = $value;
    unset($arr[$key]);
  }
  return (array)$out;
}

所以从这里:

array (
  'und' => 
  array (
    'profiles' => 
    array (
      0 => 
      array (
        'commerce_customer_address' => 
        array (
          'und' => 
          array (
            0 => 
            array (
              'first_name' => 'First name',
              'last_name' => 'Last name',
              'thoroughfare' => 'Address 1',
              'premise' => 'Address 2',
              'locality' => 'Town/City',
              'administrative_area' => 'County',
              'postal_code' => 'Postcode',
            ),
          ),
        ),
      ),
    ),
  ),
)

你会得到:

array (
  'first_name' => 'First name',
  'last_name' => 'Last name',
  'thoroughfare' => 'Address 1',
  'premise' => 'Address 2',
  'locality' => 'Town/City',
  'administrative_area' => 'County',
  'postal_code' => 'Postcode',
)