How to check if PHP array is associative or sequen

Question

PHP treats all arrays as associative, so there aren't any built in functions. Can anyone recommend a fairly efficient way to check if an array contains only numeric keys?

Basically, I want to be able to differentiate between this:

$sequentialArray = array('apple', 'orange', 'tomato', 'carrot');

and this:

$assocArray = array('fruit1' => 'apple', 
                    'fruit2' => 'orange', 
                    'veg1' => 'tomato', 
                    'veg2' => 'carrot');

Answer 1

There are many answers already, but here is the method that Laravel relies on within its Arr class:

/**
 * 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;
}

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

Answer 2

This would work too (demo):

function array_has_numeric_keys_only(array $array)
{
    try {
        SplFixedArray::fromArray($array, true);
    } catch (InvalidArgumentException $e) {
        return false;
    }
    return true;
}

Please note that the main point of this answer is to inform you about the existence of SplFixedArray and not to encourage you to use Exceptions for these kinds of tests.

Answer 3

Speed-wise:

function isAssoc($array)
{
    return ($array !== array_values($array));
}

Memory-wise:

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

Answer 4

You have asked two questions that are not quite equivalent:

• Firstly, how to determine whether an array has only numeric keys
• Secondly, how to determine whether an array has sequential numeric keys, starting from 0

Consider which of these behaviours you actually need. (It may be that either will do for your purposes.)

The first question (simply checking that all keys are numeric) is answered well by Captain kurO.

For the second question (checking whether the array is zero-indexed and sequential), you can use the following function:

function isAssoc(array $arr)
{
    if (array() === $arr) return false;
    return array_keys($arr) !== range(0, count($arr) - 1);
}

var_dump(isAssoc(array('a', 'b', 'c'))); // false
var_dump(isAssoc(array("0" => 'a', "1" => 'b', "2" => 'c'))); // false
var_dump(isAssoc(array("1" => 'a', "0" => 'b', "2" => 'c'))); // true
var_dump(isAssoc(array("a" => 'a', "b" => 'b', "c" => 'c'))); // true

Answer 5

By using xarray PHP extension

You can do this very fast (about 30+ times faster in PHP 5.6):

if (array_is_indexed($array)) {  }

Or:

if (array_is_assoc($array)) {  }

Answer 6

Surely this is a better alternative.

<?php
$arr = array(1,2,3,4);
$isIndexed = array_values($arr) === $arr;