PHP将所有数组都视为关联数组,因此没有任何内置函数。谁能推荐一种相当有效的方法来检查数组是否“是一个列表”(只包含从0开始的数字键)?

基本上,我希望能够区分这些:

$sequentialArray = [
    'apple', 'orange', 'tomato', 'carrot'
];

这:

$assocArray = [
    'fruit1' => 'apple',
    'fruit2' => 'orange',
    'veg1' => 'tomato',
    'veg2' => 'carrot'
];

当前回答

/*
iszba - Is Zero Based Array

Detects if an array is zero based or not.

PARAMS:
    $chkvfnc
        Callback in the loop allows to check the values of each element.
        Signature:
            bool function chkvfnc($v);
            return:
                true    continue looping
                false   stop looping; iszba returns false too.

NOTES:
○ assert: $array is an array.
○ May be memory efficient;
  it doesn't get extra arrays via array_keys() or ranges() into the function.
○ Is pretty fast without a callback.
○ With callback it's ~2.4 times slower.
*/
function iszba($array, $chkvfnc=null){

    $ncb = !$chkvfnc;
    $i = 0;

    foreach($array as $k => $v){
        if($k === $i++)
            if($ncb || $chkvfnc($v))
                continue;

        return false;
    }

    return true;
}

•没有回调,比当前领先的回答快30%。 而且可能内存效率更高。

•只需对答案求反,就可以知道数组是否应该被认为是关联的。

其他回答

我注意到这个问题有两种常用的方法:一种使用array_values(),另一种使用key()。为了找出哪个更快,我写了一个小程序:

$arrays = Array(
  'Array #1' => Array(1, 2, 3, 54, 23, 212, 123, 1, 1),
  'Array #2' => Array("Stack", 1.5, 20, Array(3.4)),
  'Array #3' => Array(1 => 4, 2 => 2),
  'Array #4' => Array(3.0, "2", 3000, "Stack", 5 => "4"),
  'Array #5' => Array("3" => 4, "2" => 2),
  'Array #6' => Array("0" => "One", 1.0 => "Two", 2 => "Three"),
  'Array #7' => Array(3 => "asdf", 4 => "asdf"),
  'Array #8' => Array("apple" => 1, "orange" => 2),
);

function is_indexed_array_1(Array &$arr) {
  return $arr === array_values($arr);
}

function is_indexed_array_2(Array &$arr) {
  for (reset($arr), $i = 0; key($arr) === $i++; next($arr))
    ;
  return is_null(key($arr));
}

// Method #1
$start = microtime(true);
for ($i = 0; $i < 1000; $i++) {
  foreach ($arrays as $array) {
    $dummy = is_indexed_array_1($array);
  }
}
$end = microtime(true);
echo "Time taken with method #1 = ".round(($end-$start)*1000.0,3)."ms\n";

// Method #2
$start = microtime(true);
for ($i = 0; $i < 1000; $i++) {
  foreach ($arrays as $array) {
    $dummy = is_indexed_array_2($array);
  }
}
$end = microtime(true);
echo "Time taken with method #1 = ".round(($end-$start)*1000.0,3)."ms\n";

该程序在CentOS上的PHP 5.2上的输出如下:

方法#1所花费的时间= 10.745ms 方法#2所花费的时间= 18.239ms

PHP 5.3上的输出产生了类似的结果。显然,使用array_values()要快得多。

实际上,最有效的方法是:

function is_assoc($array){
   $keys = array_keys($array);
   return $keys !== array_keys($keys);
}

这是因为它将键(对于顺序数组来说总是0,1,2等)与键的键(总是0,1,2等)进行比较。

Laravel使用这种方法。

A lot of the solutions here are elegant and pretty, but don't scale well, and are memory intensive or CPU intensive. Most are creating 2 new data points in memory with this solution from both sides of the comparison. The larger the array the harder and longer the process and memory used, and you lose the benefit of short circuit evaluation. I Did some testing with a few different ideas. Trying to avoid array_key_exists as it is costly, and also avoiding creating new large datasets to compare. I feel this is a simple way to tell if an array is sequential.

public function is_sequential( $arr = [] ){
    if( !is_array( $arr ) || empty( $arr ) ) return false;

    $i = 0;

    $total = count( $arr );

    foreach( $arr as $key => $value ) if( $key !== $i++ ) return false;

    return true;
}

在主数组上运行一个计数并存储一个整数。然后循环遍历数组并在迭代计数器时检查精确匹配。你应该从1开始计数。如果它失败了,它会短路,当它为假时,它会给你性能的提升。

最初,我这样做了一个for循环和检查isset($arr[$ I]),但这将不检测null键,这需要array_key_exists,我们知道,这是最糟糕的函数使用速度。

通过foreach不断更新变量,并检查迭代器,永远不会超过它的整数大小,让PHP使用它内置的内存优化,缓存和垃圾收集,以保持非常低的资源使用。

此外,我认为在foreach中使用array_keys是愚蠢的,因为您可以简单地运行$key => $value并检查键。为什么要创建新的数据点?一旦抽象出数组键,就会立即消耗更多内存。

Mark Amery的改进

function isAssoc($arr)
{
    // Is it set, is an array, not empty and keys are not sequentialy numeric from 0
    return isset($arr) && is_array($arr) && count($arr)!=0 && array_keys($arr) !== range(0, count($arr) - 1);
}

这个测试变量是否存在,是否为数组,是否为空数组,以及键是否从0开始连续。

来查看数组是否是关联的

if (isAssoc($array)) ...

看看它是不是数值

if (!isAssoc($array)) ...

已经有很多答案了,下面是Laravel在Arr类中依赖的方法:

/**
 * Determines if an array is associative.
 *
 * An array is "associative" if it doesn't have sequential numerical keys beginning with zero.
 *
 * @param  array  $array
 * @return bool
 */
public static function isAssoc(array $array)
{
    $keys = array_keys($array);

    return array_keys($keys) !== $keys;
}

来源:https://github.com/laravel/framework/blob/5.4/src/Illuminate/Support/Arr.php