How to check a key exists in an array in PHP ?

We have given an array arr and a Key key, the task is to check if a key exists in an array or not in PHP.

Examples:

Input : arr = ["Geek1", "Geek2", "1", "2","3"] 
 key = "2"
Output : Found the Key

Input : arr = ["Geek1", "Geek2", "1", "2","3"] 
 key = 9
Output : Key not Found

The problem can be solved using PHP inbuilt function for checking key exists in a given array. The in-built function used for the given problem are:

Method 1: Using array_key_exists() Method:

The array_key_exists() function checks whether a specific key or index is present inside an array or not.

Syntax:

boolean array_key_exists( $index, $array )

Example:

<?php // PHP program to check if a key  // exists in an array or not $array = array( 'names' => array("Geek1", "Geek2", "Geek3"), 'rank' => array('1', '2', '3') ); // Use of array_key_exists() function if(array_key_exists("rank", $array)) { echo "Found the Key"; } else{ echo "Key not Found"; } ?> 

Found the Key

Method 2: Using isset() Method:

The isset() function checks whether a specific key or index is present inside an array or not.

Syntax:

bool isset( mixed $var, mixed $... )

<?php // PHP program to check if a key  // exists in an array or not $array = array( 'names' => array("Geek1", "Geek2", "Geek3"), 'rank' => array('1', '2', '3') ); // Use of array_key_exists() function if(isset($array["rank"])){ echo "Found the Key"; } else{ echo "Key not Found"; } ?>  

Found the Key 

Method 3: Using the array_search function:

The array_search function is used to search for a given value in an array and return the corresponding key if the value is found. If the value is not found, it returns false.

Syntax:

bool = array_search($search_value, $array);

<?php $array = array('name' => 'geek', 'age' => '22'); if (array_search('geek', $array) !== false) { echo 'Found the key'; } else { echo 'Key not found'; } ?> 

Found the key

Method 4: Using array_keys

Using array_keys to check if a key exists involves getting all the keys of the array with array_keys and then using in_array to determine if the specific key is present

Example

<?php $array = ['name' => 'John', 'age' => 30, 'city' => 'New York']; $key = 'age'; if (in_array($key, array_keys($array))) { echo "Key '$key' exists in the array."; } else { echo "Key '$key' does not exist in the array."; } ?> 

Key 'age' exists in the array.

Using array_key_exists() with array_flip()

This approach involves flipping the array's keys and values using array_flip(), then using array_key_exists() to check if the key exists in the flipped array.

Example:

<?php function keyExistsUsingArrayFlip($array, $key) { $flippedArray = array_flip($array); return array_key_exists($key, $flippedArray); } // Example usage: $arr = ["Geek1", "Geek2", "1", "2", "3"]; $key = "2"; if (keyExistsUsingArrayFlip($arr, $key)) { echo "Found the Key"; } else { echo "Key not Found"; } ?> 

Found the Key

Using in_array Function Directly

The in_array function checks if a specific value exists in an array, returning true if found and false otherwise. It's used for value existence checks, not for keys.

Example

<?php $arr = ["Geek1", "Geek2", "1", "2", "3"]; $key = "2"; if (in_array($key, $arr)) { echo "Found the Key"; } else { echo "Key not Found"; } ?> 

Found the Key