How to check an array is associative or sequential in PHP?

In PHP there is no need to write the variable type before the variable because it is loosely-typed. It takes datatype from user defined values that are stored in it. Arrays in PHP is a type of data structure that allows to store multiple elements of similar data type under a single variable thereby saving the effort of creating a different variable for every data. There are basically three types of arrays in PHP:

• Sequential (Indexed) arrays
• Associative arrays
• Multidimensional arrays

Sequential Arrays: Those arrays which have numerical indexes in an ordered sequential manner (starting from 0 and ending with n-1) are called Sequential or Indexed arrays. In PHP, by default array Indexed array. php

<?php
// Example of sequential array

$arr = array("January", "February", "March");

// 1st element
echo $arr[0] . "\n";

// 2nd element
echo $arr[1] . "\n";

// 3rd element     
echo $arr[2] . "\n";
?>

Associative arrays: The arrays which are having string type keys instead of indexes or which exist in ('key', 'value')pairs are called associative arrays. php

<?php
// Example of associative array

$arr1= array("Month1" => "January",
             "Month2" => "February",
             "Month3" => "March" 
        );

echo $arr1["Month1"] . "\n";
echo $arr1["Month2"] . "\n";
echo $arr1["Month3"] . "\n";
?>

How to check if PHP array is associative or sequential? There is no inbuilt method in PHP to know the type of array. If the sequential array contains n elements then their index lies between 0 to (n-1). So find the array key value and check if it exist in 0 to (n-1) then it is sequential otherwise associative array. php

<?php
// Example to check Sequential array

// Associative array
$arr1= array("Month1" => "January",
             "Month2" => "February", 
             "Month3" => "March" 
        );
    
// Checking for sequential keys of array arr
if(array_keys($arr1) !== range(0, count($arr1) - 1))
    echo "Array is associative"; 
else
    echo "Array is sequential \n";
?>

Note:

• === It returns True if $x and $y are equal and same type.
• !== It returns True if $x and $y are not equal or not same type.
• == It returns True if $x and $y are equal.
• != It returns True if $x not equal to $y.