A benchmark of several methods for checking if PHP array is associative

isAssocArrayBench.php

<?php
if(!isset($argv[1])){
    echo "Usage: ".$argv[0]." (number of iterations)\n";
    exit(1);
}

/**
 * Arrays to check
 */
$tests = array(
    array(array(
        'foo' => 'bar',
    )),
    array(array(
        'bar',
        'foo' => 'bar',
        'baz',
    )),
    array(null),
    array(true),
    array(false),
    array(0),
    array(1),
    array(0.0),
    array(1.0),
    array('string'),
    array(array(0, 1, 2)),
    array(new stdClass),
    array_fill(0,1000,uniqid()),                // big numeric array

    array_fill_keys(range(2,1000,3),uniqid()),  // big misaligned numeric array (=associative)

    array_fill_keys(                            // big associative array
        str_split(
            str_repeat(uniqid('',true),100),
            3
        ),
        true
    )
);

$iterations = (int)$argv[1];

/**
 * Common methods to check associative array
 */
$methods = array(
    'method1 (array_values check)' =>
        function($array){
            return (array_values($array) !== $array);
        },

    'method2 (array_keys comparison)' =>
        function($array){
            $array = array_keys($array); return ($array !== array_keys($array));
        },

    'method3 (array_filter of keys)' =>
        function($array){
            return count(array_filter(array_keys($array), 'is_string')) > 0;
        }
);

/**
 * Perform benchmark on each method
 */
foreach($methods as $name=>$func){
    echo "Testing $name - $iterations iterations\n";
    $time = microtime(true);

    for($x=0;$x<$iterations;$x++){
        foreach($tests as $array){
            $func($array);
        }
    }

    /**
     * Show results
     */
    $totalTime = (microtime(true) - $time);
    $avgTime = $totalTime / ($iterations * count($tests));

    echo "  Total time: ".number_format($totalTime,5,'.',' ')." s\n";
    echo "  Average   : ".number_format($avgTime*1000,5,'.',' ')." ms / test \n";
    echo "\n";
}

check this out:

$methods = [
 
    // [...]

    'method4 (revision of method1, with php8.1 fn)' =>
       function ($array) {
            return (array_is_list($array) === false);
        },

    'method5 (json_encode output parsing with array_is_list - php>=8.1)' =>
       static function ($array) {
            // consider empty, and [0, 1, 2, ...] sequential
            if (empty($array) || array_is_list($array)) {
                return false;
            }

            // first scenario:
            // [  1  => [*any*] ]
            // [ 'a' => [*any*] ]
            foreach ( $array as $key => $value ) {
                if (is_array($value)) {
                    return true;
                }
            }

            // second scenario: read the json string
            $jsonNest = json_encode($array, JSON_THROW_ON_ERROR);

            return str_contains($jsonNest, '{');
        },


    'method6 (json_encode output parsing - php=8.0)' =>
       static function ($array) {

            if (empty($array) || array_values($array) !== $array) { return false; }

            foreach ( $array as $key => $value ) { if (is_array($value)) { return true; } }
            
            $jsonNest = json_encode($array, JSON_THROW_ON_ERROR);

            return str_contains($jsonNest, '{');
        },

];

Results

Testing method1 (array_values check) - 10000 iterations
  Total time: 0.60444 s
  Average   : 0.00403 ms / test 

Testing method2 (array_keys comparison) - 10000 iterations
  Total time: 0.32689 s
  Average   : 0.00218 ms / test 

Testing method3 (array_filter of keys) - 10000 iterations
  Total time: 2.22523 s
  Average   : 0.01483 ms / test 

Testing method4 (revision of method1, with php8.1 fn) - 10000 iterations
  Total time: 0.09834 s
  Average   : 0.00066 ms / test 

Testing method5 (json_encode output parsing with array_is_list - php>=8.1) - 10000 iterations
  Total time: 0.47469 s
  Average   : 0.00316 ms / test

Testing method6 (json_encode output parsing - php<=8.0) - 10000 iterations
  Total time: 1.01134 s
  Average   : 0.00674 ms / test 

Anyone curious about the benchmark without the static closure?

Testing method5 (json_encode output parsing with array_is_list - php>=8.1) - 10000 iterations
  Total time: 1.08914 s
  Average   : 0.00726 ms / test 

Testing method6 (json_encode output parsing - php=8.0) - 10000 iterations
  Total time: 4.92953 s
  Average   : 0.03286 ms / test 

They are much slower!

other methods perform the same instead. Somebody can explain me why?