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

function isAssoc($arr)
{
    $a = array_keys($arr);
    for($i = 0, $t = count($a); $i < $t; $i++)
    {
        if($a[$i] != $i)
        {
            return false;
        }
    }
    return true;
}

其他回答

我认为标量数组的定义因应用程序而异。也就是说,一些应用程序将需要更严格的定义标量数组,而一些应用程序将需要更宽松的定义。

下面我将介绍3种不同严格程度的方法。

<?php
/**
 * Since PHP stores all arrays as associative internally, there is no proper
 * definition of a scalar array.
 * 
 * As such, developers are likely to have varying definitions of scalar array,
 * based on their application needs.
 * 
 * In this file, I present 3 increasingly strict methods of determining if an
 * array is scalar.
 * 
 * @author David Farrell <DavidPFarrell@gmail.com>
 */

/**
 * isArrayWithOnlyIntKeys defines a scalar array as containing
 * only integer keys.
 * 
 * If you are explicitly setting integer keys on an array, you
 * may need this function to determine scalar-ness.
 * 
 * @param array $a
 * @return boolean
 */ 
function isArrayWithOnlyIntKeys(array $a)
{
    if (!is_array($a))
        return false;
    foreach ($a as $k => $v)
        if (!is_int($k))
            return false;
    return true;
}

/**
 * isArrayWithOnlyAscendingIntKeys defines a scalar array as
 * containing only integer keys in ascending (but not necessarily
 * sequential) order.
 * 
 * If you are performing pushes, pops, and unsets on your array,
 * you may need this function to determine scalar-ness.
 * 
 * @param array $a
 * @return boolean
 */ 
function isArrayWithOnlyAscendingIntKeys(array $a)
{
    if (!is_array($a))
        return false;
    $prev = null;
    foreach ($a as $k => $v)
    {
        if (!is_int($k) || (null !== $prev && $k <= $prev))
            return false;
        $prev = $k;
    }
    return true;
}

/**
 * isArrayWithOnlyZeroBasedSequentialIntKeys defines a scalar array
 * as containing only integer keys in sequential, ascending order,
 * starting from 0.
 * 
 * If you are only performing operations on your array that are
 * guaranteed to either maintain consistent key values, or that
 * re-base the keys for consistency, then you can use this function.
 * 
 * @param array $a
 * @return boolean
 */
function isArrayWithOnlyZeroBasedSequentialIntKeys(array $a)
{
    if (!is_array($a))
        return false;
    $i = 0;
    foreach ($a as $k => $v)
        if ($i++ !== $k)
            return false;
    return true;
}

下面是我使用的方法:

function is_associative ( $a )
{
    return in_array(false, array_map('is_numeric', array_keys($a)));
}

assert( true === is_associative(array(1, 2, 3, 4)) );

assert( false === is_associative(array('foo' => 'bar', 'bar' => 'baz')) );

assert( false === is_associative(array(1, 2, 3, 'foo' => 'bar')) );

注意,这并不包括特殊情况,如:

$a = array( 1, 2, 3, 4 );

unset($a[1]);

assert( true === is_associative($a) );

对不起,我帮不了你。对于大小合适的数组,它也有一定的性能,因为它不会产生不必要的拷贝。正是这些小细节使得Python和Ruby编写起来更加方便……: P

function isAssoc($arr)
{
    $a = array_keys($arr);
    for($i = 0, $t = count($a); $i < $t; $i++)
    {
        if($a[$i] != $i)
        {
            return false;
        }
    }
    return true;
}

我比较数组的键值和数组的array_values()结果的键值之间的差异,数组始终是一个具有整数下标的数组。如果键是相同的,它就不是一个关联数组。

function isHash($array) {
    if (!is_array($array)) return false;
    $diff = array_diff_assoc($array, array_values($array));
    return (empty($diff)) ? false : true;
}

PHP 8.1增加了一个内置函数来确定数组是否是具有这些语义的列表。函数是array_is_list:

$list = ["a", "b", "c"];

array_is_list($list); // true

$notAList = [1 => "a", 2 => "b", 3 => "c"];

array_is_list($notAList); // false

$alsoNotAList = ["a" => "a", "b" => "b", "c" => "c"];

array_is_list($alsoNotAList); // false

参考