Removing duplicate elements from an array in PHP

In PHP, there are several methods to remove duplicate elements from an array. The most common approaches include using array_unique(), array_flip(), or array_keys() with array_count_values().

Using array_flip()

The array_flip() function reverses keys and values. When flipped twice, duplicate values are automatically removed since array keys must be unique −

<?php
   $my_arr = array(45, 65, 67, 99, 81, 90, 99, 45, 68);
   echo "The original array contains <br>";
   print_r($my_arr);
   
   $my_arr = array_flip($my_arr);
   $my_arr = array_flip($my_arr);
   $my_arr = array_values($my_arr);
   
   echo "\nThe array after removing duplicate elements is <br>";
   print_r($my_arr);
?>

The original array contains
Array
(
   [0] => 45
   [1] => 65
   [2] => 67
   [3] => 99
   [4] => 81
   [5] => 90
   [6] => 99
   [7] => 45
   [8] => 68
)

The array after removing duplicate elements is
Array
(
   [0] => 45
   [1] => 65
   [2] => 67
   [3] => 99
   [4] => 81
   [5] => 90
   [6] => 68
)

Using array_unique()

The simplest method is using PHP's built-in array_unique() function −

<?php
   $my_arr = array(45, 65, 67, 99, 81, 90, 99, 45, 68);
   echo "Original array:<br>";
   print_r($my_arr);
   
   $unique_arr = array_unique($my_arr);
   $unique_arr = array_values($unique_arr); // Re-index array
   
   echo "\nAfter removing duplicates:<br>";
   print_r($unique_arr);
?>

Original array:
Array
(
   [0] => 45
   [1] => 65
   [2] => 67
   [3] => 99
   [4] => 81
   [5] => 90
   [6] => 99
   [7] => 45
   [8] => 68
)

After removing duplicates:
Array
(
   [0] => 45
   [1] => 65
   [2] => 67
   [3] => 99
   [4] => 81
   [5] => 90
   [6] => 68
)

Comparison

Conclusion

Use array_unique() for simplicity or array_flip() for better performance with large arrays. Both methods effectively remove duplicates while preserving the first occurrence of each unique value.