Check and return duplicates array php

You can get the difference of the original array and a copy without duplicates using array_unique and array_diff_assoc:

array_diff_assoc($arr, array_unique($arr))

function array_dup($ar){
   return array_unique(array_diff_assoc($ar,array_unique($ar)));
}

Should do the trick.

You can do like this:

function showDups($array)
{
  $array_temp = array();

   foreach($array as $val)
   {
     if (!in_array($val, $array_temp))
     {
       $array_temp[] = $val;
     }
     else
     {
       echo 'duplicate = ' . $val . '<br />';
     }
   }
}


$array = array(1,2,2,4,5);
showDups($array);

Output:

duplicate = 2

in addition to gumbo's answer:

function returndup($arr)
{
  return array_diff_key($arr, array_unique($arr));
}

function returndup($array) 
{
    $results = array();
    $duplicates = array();
    foreach ($array as $item) {
        if (in_array($item, $results)) {
            $duplicates[] = $item;
        }

        $results[] = $item;
    }

    return $duplicates;
}

I did some tests and indeed @user187291's variant is the fastest. But, it turns out that @Gumbo's and @faebser's alternative are almost as fast, @faebser's being just slightly faster than @Gumbo's and sometimes even fastest of all.

Here's the code I used

$array = array(1, "hello", 1, "world", "hello");
$times = 1000000;

$start = microtime(true);
for ($i = 0; $i < $times; $i++) {
    $dups = array();
    foreach(array_count_values($array) as $val => $c)
        if( $c > 1) $dups[] = $val;
}
$end = microtime(true);

echo 'variant 1 (user187291): ' . ($end - $start);
echo '<br><br><br>';

$start = microtime(true);
for ($i = 0; $i < $times; $i++)
    $dups = array_unique(array_diff_assoc($array, array_unique($array)));
$end = microtime(true);

echo 'variant 2 (JAL): ' . ($end - $start);
echo '<br><br><br>';

$start = microtime(true);
for ($i = 0; $i < $times; $i++)
    $dups = array_diff_assoc($array, array_unique($array));
$end = microtime(true);

echo 'variant 3 (Gumbo): ' . ($end - $start);
echo '<br><br><br>';

$start = microtime(true);
for ($i = 0; $i < $times; $i++)
    $dups = array_diff_key($array, array_unique($array));
$end = microtime(true);

echo 'variant 4 (faebser): ' . ($end - $start);
echo '<br><br><br>';

I have found another way to return duplicates in an array

function printRepeating($arr, $size) 
{ 
    $i; 
    $j; 
    for($i = 0; $i < $size; $i++) 
        for($j = $i + 1; $j < $size; $j++) 
            if($arr[$i] == $arr[$j]) 
                echo $arr[$i], " "; 
}  



printRepeating($array, sizeof($array,0);

If you need a solution that will work with an array of arrays (or any array values other than integers or strings) try this:

function return_dup( $arr ) {
    $dups = array();
    $temp = $arr;
    foreach ( $arr as $key => $item ) {
        unset( $temp[$key] );
        if ( in_array( $item, $temp ) ) {
            $dups[] = $item;
        }
    }
    return $dups;
}


$arr = array(
    array(
        0 => 'A',
        1 => 'B',
    ),
    array(
        0 => 'A',
        1 => 'B',
    ),
    array(
        0 => 'C',
        1 => 'D',
    ),
    array(
        0 => 'C',
        1 => 'D',
    ),
    array(
        0 => 'E',
        1 => 'F',
    ),
    array(
        0 => 'F',
        1 => 'E',
    ),
    array(
        0 => 'Y',
        1 => 'Z',
    ),
);

var_export( return_dup( $arr ) );
/*
array (
    0 => array (
        0 => 'A',
        1 => 'B',
    ),
    1 => array (
        0 => 'C',
        1 => 'D',
    ),
)
*/

As per your problem if you have duplicate values then you have to return those values. I write a function for this problem. If your array has duplicate values this function returns these values within the array otherwise it returns null values. Here is an example:

function containsDuplicate($array_values) {
    $duplicates_values = [];
    for($i = 0; $i < count($array_values); $i++){
        for ($j=$i+1; $j <count($array_values) ; $j++) { 
            if ($array_values[$i] == $array_values[$j]) {
                $duplicates_values[] =  $array_values[$i];
            }
        }
    
    }
    if(count($duplicates_values) > 0){
        return $duplicates_values;
    }
}