Check and return duplicates array php - php

Question

I would like to check if my array has any duplicates and return the duplicated values in an array.
I want this to be as efficient as possible.
Example:
$array = array( 1, 2, 2, 4, 5 );
function return_dup($array); // should return 2
$array2 = array( 1, 2, 1, 2, 5 );
function return_dup($array2); // should return an array with 1,2
Also the initial array is always 5 positions long

Answer 1

this will be ~100 times faster than array_diff
$dups = array();
foreach(array_count_values($arr) as $val => $c)
if($c > 1) $dups[] = $val;

Answer 2

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))

Answer 3

function array_dup($ar){
return array_unique(array_diff_assoc($ar,array_unique($ar)));
}
Should do the trick.

Answer 4

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

Answer 5

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

Answer 6

in addition to gumbo's answer:
function returndup($arr)
{
return array_diff_key($arr, array_unique($arr));
}

Answer 7

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>';

Answer 8

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);

Answer 9

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',
),
)
*/

Answer 10

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;
}
}

Answer 11

$duplicate_array = array();
for($i=0;$i<count($array);$i++){
for($j=0;$j<count($array);$j++){
if($i != $j && $array[$i] == $array[$j]){
if(!in_array($array[$j], $duplicate_array)){
$duplicate_array[] = $array[$j];
}
}
}
}