PHP Array Exercises : Identify the email addresses which are not unique

Last update on May 30 2025 13:13:56 (UTC/GMT +8 hours)

41. Identify Non-Unique Email Addresses

Write a PHP program to identify the email addresses which are not unique.

Sample Solution:

PHP Code:

<?php
// Define a function to find non-unique values in an array
function array_not_unique($my_array) {
    // Initialize an array to store duplicate values
    $same = array();
    
    // Perform a natural case-insensitive sort on the array
    natcasesort($my_array);
    
    // Reset the array pointer to the beginning
    reset($my_array);

    // Initialize variables to track the previous key and value
    $old_key    = NULL;
    $old_value    = NULL;

    // Loop through the sorted array to find duplicate values
    foreach ($my_array as $key => $value) {
        // Skip NULL values
        if ($value === NULL) { continue; }

        // Check if the current value is the same as the previous value
        if ($old_value == $value) {
            // Store the duplicate values and their corresponding keys
            $same[$old_key]    = $old_value;
            $same[$key]        = $value;
        }

        // Update the variables with the current key and value
        $old_value    = $value;
        $old_key    = $key;
    }

    // Return the array containing non-unique values
    return $same;
}

// Create a test array with duplicate and non-duplicate values
$test_array = array();
$test_array[1]    = '[email protected]';
$test_array[2]    = '[email protected]';
$test_array[3]    = '[email protected]';
$test_array[4]    = '[email protected]';

// Call the function and display the result
print_r(array_not_unique($test_array));
?>

Output:

Array                                                               
(                                                                   
    [1] => [email protected]                                          
    [3] => [email protected]                                          
)

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP script to scan an array of email addresses and return those that appear more than once.
Write a PHP function that takes an array of emails, identifies duplicates, and outputs them in a list.
Write a PHP program to use array_count_values() to count email occurrences and display non-unique entries.
Write a PHP script to compare an array of email addresses and output a boolean indicating if any duplicates exist.

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