PHP Array Exercises : Create a multidimensional unique array for any single key index

Last update on May 30 2025 13:14:44 (UTC/GMT +8 hours)

38. Multidimensional Unique Array by Key Index

Write a PHP function to create a multidimensional unique array for any single key index.

Sample Solution:

PHP Code:

<?php
// Define a function to filter unique values based on a specified key in a multidimensional array
function unique_array($my_array, $key) { 
    $result = array();   // Initialize an empty array to store the unique values
    $i = 0;              // Initialize a counter
    $key_array = array(); // Initialize an array to keep track of encountered keys
    
    // Iterate through each element in the input array
    foreach($my_array as $val) { 
        // Check if the key value is not already present in the key array
        if (!in_array($val[$key], $key_array)) { 
            $key_array[$i] = $val[$key];  // Store the key value in the key array
            $result[$i] = $val;           // Store the entire element in the result array
        } 
        $i++;  // Increment the counter
    } 
    
    // Return the array containing unique values based on the specified key
    return $result; 
}  

// Define an array of students with associated information
$students = array( 
    0 => array("city_id"=>"1", "name"=>"Sara",  "mobile_num"=>"1111111111"), 
    1 => array("city_id"=>"2", "name"=>"Robin", "mobile_num"=>"2222222222"), 
    2 => array("city_id"=>"1", "name"=>"Sonia", "mobile_num"=>"3333333333"), 
); 

// Display the result of applying the unique_array function to the students array with the "city_id" key
print_r(unique_array($students, "city_id"));

?>

Output:

Array                                                       
(                                                           
    [0] => Array                                            
        (                                                   
            [city_id] => 1                                  
            [name] => Sara                                  
            [mobile_num] => 1111111111                      
        )                                                   
                                                            
    [1] => Array                                            
        (                                                   
            [city_id] => 2                                  
            [name] => Robin                                 
            [mobile_num] => 2222222222                      
        )                                                   
                                                            
)

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP function to remove duplicate sub-arrays from a multidimensional array based on a single key index.
Write a PHP script to iterate over a multidimensional array and build a new array containing only unique values for a specified key.
Write a PHP program to compare key values across sub-arrays and filter out duplicates to create a unique multidimensional array.
Write a PHP function to generate a flattened array from a multidimensional input while ensuring uniqueness of a specified key.

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