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How to Check if a Key Exists in an Associative Array in PHP?

Given an Associative array, the task is to check whether a key exists in the associative array or not. There are two methods to check if a key exists in an associative array, these are – using array_key_exists(), and isset() functions. Let’s explore each method with detailed explanations and code examples.

Table of Content

Approach 1: Using array_key_exists() Function

The array_key_exists() function checks if a specified key exists in an array. It returns true if the key exists and false otherwise.

PHP 
<?php

$student_marks = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

// Check if the key exists in the array
if (array_key_exists('Physics', $student_marks)) {
    echo "Key exists in the array";
} else {
    echo "Key does not exist in the array";
}

?>

Output
Key exists in the array

Approach 2: Using isset() Function

The isset() function checks if a variable is set and is not null. When used with an array, it checks if a specified key exists in the array and is not null.

PHP 
<?php

$student_marks = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

// Check if the key exists in the array
if (isset($student_marks['Physics'])) {
    echo "Key exists in the array";
} else {
    echo "Key does not exist in the array";
}

?>

Output
Key exists in the array

Approach 3: Using array_key_first() Function

The array_key_first() function returns the first key of the given array. We can use this function to determine if a key exists by iterating over the keys of the array.

PHP 
<?php
$student_marks = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

// Check if the key exists in the array
function keyExists($key, $array) {
    foreach (array_keys($array) as $k) {
        if ($k === $key) {
            return true;
        }
    }
    return false;
}

if (keyExists('Physics', $student_marks)) {
    echo "Key exists in the array";
} else {
    echo "Key does not exist in the array";
}

?>

Output
Key exists in the array

Approach 4 : Looping through Keys

To check if a key exists in an associative array in PHP, iterate through array keys using a foreach loop. Compare each key against the target key. Set a flag upon finding a match to confirm existence or absence of the key.

Example:

PHP 
<?php
// Associative array
$assocArray = [
    "key1" => "value1",
    "key2" => "value2",
    "key3" => "value3",
];

// Key to search for
$findKey = "key2";

// Flag to indicate key existence
$keyExists = false;

// Loop through keys
foreach ($assocArray as $key => $value) {
    if ($key === $findKey) {
        $keyExists = true;
        break;
    }
}

// Output results
if ($keyExists) {
    echo "Key '$findKey' exists in the associative array.";
} else {
    echo "Key '$findKey' does not exist in the associative array.";
}
?>

Output
Key 'key2' exists in the associative array.

Approach 5: Using the in_array() Function with array_keys()

The in_array() function checks if a value exists in an array. By combining it with the array_keys() function, which returns all the keys of an array, you can check if a specific key exists.

Example

PHP 
<?php
$array = array(
    "first" => 1,
    "second" => 2,
    "third" => 3
);

$keyToCheck = "second";

if (in_array($keyToCheck, array_keys($array))) {
    echo "Key '$keyToCheck' exists in the array.";
} else {
    echo "Key '$keyToCheck' does not exist in the array.";
}
?>

Output
Key 'second' exists in the array.

 


Reffered: https://www.geeksforgeeks.org

PHP

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Type:
 Geek
Category:
 Coding
Sub Category:
 Tutorial
Uploaded by:
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