How to detect duplicate values in PHP array?

I am working with a one dimensional array in PHP. I would like to detect the presence of duplicate values, then count the number of duplicate values and out put the results. For example, given the following array:

$array = array('apple', 'orange', 'pear', 'banana', 'apple', 'pear', 'kiwi', 'kiwi', 'kiwi'); 

I would like to print:

apple (2) orange pear (2) banana kiwi (3) 

Any advice on how to approach this problem?

Thanks.

Mike

13 Answers

You can use array_count_values function

$array = array('apple', 'orange', 'pear', 'banana', 'apple', 'pear', 'kiwi', 'kiwi', 'kiwi'); print_r(array_count_values($array)); 

will output

Array ( [apple] => 2 [orange] => 1 [pear] => 2 etc... ) 

if(count(array_unique($array))<count($array)) { // Array has duplicates } else { // Array does not have duplicates } 

function array_not_unique( $a = array() ) { return array_diff_key( $a , array_unique( $a ) ); } 

You could try turning that array into a associative array with the fruits as keys and the number of occurrences as values. Bit long-winded, but it looks like:

$array = array('apple', 'orange', 'pear', 'banana', 'apple', 'pear', 'kiwi', 'kiwi', 'kiwi'); $new_array = array(); foreach ($array as $key => $value) { if(isset($new_array[$value])) $new_array[$value] += 1; else $new_array[$value] = 1; } foreach ($new_array as $fruit => $n) { echo $fruit; if($n > 1) echo "($n)"; echo "<br />"; } 

To get rid use array_unique(). To detect if have any use count(array_unique()) and compare to count($array).

Stuff them into a map (pseudocode)

map[string -> int] $m foreach($word in $array) { if(!$m.contains($word)) $m[$word] = 0; $m[$word] += 1; } 

Perhaps something like this (untested code but should give you an idea)?

$new = array(); foreach ($array as $value) { if (isset($new[$value])) $new[$value]++; else $new[$value] = 1; } 

Then you'll get a new array with the values as keys and their value is the number of times they existed in the original array.

I didn't find the answer I was looking for, so I wrote this function. This will make an array that contains only the duplicates between the two arrays, but not print the number of times an element is duplicated, so it's not directly answering the question, but I'm hoping it'll help someone in my situation.

function findDuplicates($array1,$array2) { $combined = array_merge($array1,$array2); $counted = array_count_values($combined); $dupes = []; $keys = array_keys($counted); foreach ($keys as $key) { if ($counted[$key] > 1) {$dupes[] = $key;} } sort($dupes); return $dupes; } $array1 = [1,2,3,4,5]; $array2 = [4,5,6,7,8]; $dupes = findDuplicates($array1,$array2); print_r($dupes); 

Outputs:

Array ( [0] => 4 [1] => 5 ) 

$data = ['outer', 'inner', 'sole', 'sole', 'outer', 'outer']; $result = max(array_count_values($data)); if($result > 1) { echo 'Duplicate items were found!'; } 

I think this way is shorter and cleaner.

function array_not_unique(array $array): array { $duplicate_array = array_diff_key( $array , array_unique( $array ) ); $unique_array = []; foreach ($array as $key => $value) { if ( in_array($value, $duplicate_array)) { $duplicate_array[$key] = $value; } else { $unique_array[$key] = $value; } } return ["unique_array" => $unique_array, "duplicate_array" => $duplicate_array]; } 

$count = 0; $output =''; $ischeckedvalueArray = array(); for ($i=0; $i < sizeof($array); $i++) { $eachArrayValue = $array[$i]; if(! in_array($eachArrayValue, $ischeckedvalueArray)) { for( $j=$i; $j < sizeof($array); $j++) { if ($array[$j] === $eachArrayValue) { $count++; } } $ischeckedvalueArray[] = $eachArrayValue; $output .= $eachArrayValue. " Repated ". $count."<br/>"; $count = 0; } } echo $output; 

This function give you the redundant values only

function array_find_redundant($A){ $U=$N=[]; foreach($A As $k=>$v){ if(in_array($v,$U)){$N[$k]=$v;}else{$U[]=$v;} } return $N; } $A = ['A','B','B','C','C','C']; $B = array_find_redundant($A); // [2=>'B',4=>'C',5=>'C'] 

A simple method:

$array = array_values(array_unique($array, SORT_REGULAR));