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krsort sorting does not take effect? Solve FAQs

gitbox 2025-05-27

1. Review of the basic usage of krsort()

 <?php
$array = [
    "b" => 2,
    "a" => 1,
    "c" => 3,
];
krsort($array);
print_r($array);
?>

After running, the output result:

 Array
(
    [c] => 3
    [b] => 2
    [a] => 1
)

Here, the key names are sorted from large to small by letter, which meets expectations.

2. Common reasons why krsort() does not take effect

1. The key name type is not uniform

When krsort() sorts by key names, the key names will be automatically treated as strings or integers. If the key names of the array are mixed, the sorting result may not be as expected.

For example:

 <?php
$array = [
    2 => 'two',
    "10" => 'ten',
    1 => 'one',
];
krsort($array);
print_r($array);
?>

At this time, the key name 10 is a string but is actually a numeric key, which will be converted into an integer processing, which may cause the sorting order to be inconsistent with the expected one.

2. The multidimensional array does not specify the sorting level

krsort() only sorts the first layer key names of the array. If it is a multidimensional array, the internal subarray will not be sorted.

 <?php
$array = [
    "first" => ["b" => 2, "a" => 1],
    "second" => ["d" => 4, "c" => 3],
];
krsort($array);
print_r($array);
?>

Here we will only sort the first-level key names, first and second , and the internal key names of b, a, d, and c will not change.

3. Incorrect variable type

krsort() only supports array parameters. If a non-array (such as an object or a string) is passed in, the function will not work and may even report an error.

3. How to troubleshoot the problem that krsort() does not take effect?

  1. Check if the variable is an array

Use the is_array() function to verify to avoid misuse.

 if (!is_array($array)) {
    echo "The variable passed in is not an array，Unable to sort";
}

  1. Check if the key name type is consistent

Check whether the key names are all strings or integers to avoid mixing and causing sorting exceptions.

 foreach ($array as $key => $value) {
    var_dump($key, gettype($key));
}

  1. Confirm whether the expected hierarchy is sorted

For multi-dimensional arrays, it is necessary to clarify which layer you need to sort.

IV. Solution examples

Several solutions are given to the above problems:

1. Force the key name to string

If the key names are mixed, the key name type is unified first:

 <?php
$newArray = [];
foreach ($array as $key => $value) {
    $newArray[(string)$key] = $value;
}
krsort($newArray);
print_r($newArray);
?>

This avoids confusion of numeric strings.

2. Recursively sort multidimensional arrays

If you need to sort the subarray key names as well, use the recursive method:

 <?php
function recursive_krsort(&$array) {
    if (!is_array($array)) return;
    krsort($array);
    foreach ($array as &$value) {
        if (is_array($value)) {
            recursive_krsort($value);
        }
    }
}

recursive_krsort($array);
print_r($array);
?>

3. Confirm the variable to be an array

 <?php
if (is_array($array)) {
    krsort($array);
} else {
    echo "Variables are not arrays，Unable to sort。";
}
?>

5. Practical reference link

For more detailed instructions and examples about PHP krsort() , you can access the official documentation:

<code> https://gitbox.net/manual/en/function.krsort.php </code>

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