How to remove all instances of duplicated values from an array

Question

I know there is array_unique function, but I want to remove duplicates. Is there a built-in function or do I have to roll my own.

Example input:

banna, banna, mango, mango, apple

Expected output:

apple

Answer 1

You can use

$singleOccurences = array_keys(
    array_filter(
        array_count_values(
            array('banana', 'mango', 'banana', 'mango', 'apple' )
        ),
        function($val) {
            return $val === 1;
        }
    )
)

See

• array_count_values — Counts all the values of an array
• array_filter — Filters elements of an array using a callback function
• array_keys — Return all the keys or a subset of the keys of an array
• callbacks

Answer 2

PHP.net http://php.net/manual/en/function.array-unique.php

array array_unique ( array $array [, int $sort_flags = SORT_STRING ] )

Takes an input array and returns a new array without duplicate values.

---

New solution:

function remove_dupes(array $array){
    $ret_array = array();
    foreach($array as $key => $val){
        if(count(array_keys($val) > 1){
            continue;
        } else { 
            $ret_array[$key] = $val; 
        }
}

Answer 3

If you want to only leave values in the array that are already unique, rather than select one unique instance of each value, you will indeed have to roll your own. Built in functionality is just there to sanitise value sets, rather than filter.

Answer 4

You want to remove any entries that have duplicates, so that you're left with only the entries that were unique in the list? Hmm it does sound like something you'll need to roll your own.

Answer 5

There is no existing function; You'll have to do this in two passes, one to count the unique values and one to extract the unique values:

$count = array();
foreach ($values as $value) {
  if (array_key_exists($value, $count))
    ++$count[$value];
  else
    $count[$value] = 1;
}

$unique = array();
foreach ($count as $value => $count) {
  if ($count == 1)
    $unique[] = $value;
}

Answer 6

Just write your own simple foreach loop:

$used = array();    
$array = array("banna","banna","mango","mango","apple");

foreach($array as $arrayKey => $arrayValue){
    if(isset($used[$arrayValue])){
        unset($array[$used[$arrayValue]]);
        unset($array[$arrayKey]);
    }
    $used[$arrayValue] = $arrayKey;
}
var_dump($array); // array(1) { [4]=>  string(5) "apple" } 

have fun :)

Answer 7

You can built a function based on array_count_values.

$array = array( "banana","banana","mango","mango","apple" );

$value_count_array = array_count_values( $array );
$value_one_count_array = array_filter( $value_count_array, function ( $value_count ) { return $value_count == 1; } );
$unique_values_only_array = array_keys( $value_one_count_array );

print_r( $unique_values_only_array ); //Array ( [0] => apple )

Also in one line

$unique_values_only_array = array_keys( array_filter( array_count_values( $array ), function ( $value_count ) { return $value_count == 1; } ) );

Answer 8

You can use a combination of array_unique, array_diff_assoc and array_diff:

array_diff($arr, array_diff_assoc($arr, array_unique($arr)))

Answer 9

The answer on top looks great, but on a side note: if you ever want to eliminate duplicates but leave the first one, using array_flip twice would be a pretty simple way to do so. array_flip(array_flip(x))