How to Check if a Key Exists in an Associative Array in PHP?
Last Updated : 16 Jul, 2024
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.
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"; } ?> OutputKey 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"; } ?> OutputKey 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"; } ?> OutputKey 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."; } ?> OutputKey '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."; } ?> OutputKey 'second' exists in the array.
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