从PHP 5.3开始，最短的解决方案似乎是array_walk_recursive()与新的闭包语法:

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

这个版本可以做深层、浅层或特定数量的层:

/**
 * @param  array|object $array  array of mixed values to flatten
 * @param  int|boolean  $level  0:deep, 1:shallow, 2:2 levels, 3...
 * @return array
 */
function flatten($array, $level = 0) {
    $level = (int) $level;
    $result = array();
    foreach ($array as $i => $v) {
        if (0 <= $level && is_array($v)) {
            $v = flatten($v, $level > 1 ? $level - 1 : 0 - $level);
            $result = array_merge($result, $v);
        } elseif (is_int($i)) {
            $result[] = $v;
        } else {
            $result[$i] = $v; 
        }
    }
    return $result;
}

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>

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));

如果你想保留中间键:

function flattenArray(array &$result, $value, string $key = "")
{
    if (!is_array($value)) {
        $result[$key] = $value;
        return $result;
    }
    foreach ($value as $subKey => $subArray) {
        $newKey = $key !== "" ? $key . "_" . $subKey : $subKey;
        flattenArray($result, $subArray, $newKey);
    }
    return $result;
}

$nestedArray = [
    "name" => "John",
    "pets" => [
        ["id" => 1, "name" => "snooop"],
        ["id" => 2, "name" => "medor"],
    ],
    "job" => ["title" => "developper"],
];

$intermediateResult = [];
$flattened = flattenArray($intermediateResult, $nestedArray);
var_dump($flattened);

这将输出:

array(6) {
["name"]=>
  string(4) "John"
        ["pets_0_id"]=>
  int(1)
  ["pets_0_name"]=>
  string(6) "snooop"
        ["pets_1_id"]=>
  int(2)
  ["pets_1_name"]=>
  string(5) "medor"
        ["job_title"]=>
  string(10) "developper"
}

看到https://ideone.com/KXLtzZ stdout

从PHP v7.4开始，可以使用展开操作符并合并数组。简单有效。

$flatArr = array_merge(...$originalArray);