CODEWITHSUNDEEP
phparraysduplicates
Mala
Mala

Reputation: 14803

php: check if an array has duplicates

I'm sure this is an extremely obvious question, and that there's a function that does exactly this, but I can't seem to find it. In PHP, I'd like to know if my array has duplicates in it, as efficiently as possible. I don't want to remove them like array_unique does, and I don't particularly want to run array_unique and compare it to the original array to see if they're the same, as this seems very inefficient. As far as performance is concerned, the "expected condition" is that the array has no duplicates.

I'd just like to be able to do something like

if (no_dupes($array))
    // this deals with arrays without duplicates
else
    // this deals with arrays with duplicates

Is there any obvious function I'm not thinking of?
How to detect duplicate values in PHP array?
has the right title, and is a very similar question, however if you actually read the question, he's looking for array_count_values.

Upvotes: 95

Views: 156228

Answers (18)

Jekis
Jekis

Reputation: 4685

The shortest one

function no_dupes($array) {
    return $array === array_unique($array);
}

Upvotes: 0

s3m3n
s3m3n

Reputation: 4197

Performance-Optimized Solution

If you care about performance and micro-optimizations, check this one-liner:

function no_dupes(array $input_array) {
    return count($input_array) === count(array_flip($input_array));
}

Description:
Function compares number of array elements in $input_array with array_flip'ed elements. Values become keys and guess what - keys must be unique in associative arrays so not unique values are lost and final number of elements is lower than original.

Warning:
As noted in the manual, array keys can be only type of int or string so this is what you must have in original array values to compare, otherwise PHP will start casting with unexpected results. See https://3v4l.org/7bRXI for an example of this fringe-case failure mode.

Proof for an array with 10 million records:

Test case:

<?php

$elements = array_merge(range(1,10000000),[1]);

$time = microtime(true);
accepted_solution($elements);
echo 'Accepted solution: ', (microtime(true) - $time), 's', PHP_EOL;

$time = microtime(true);
most_voted_solution($elements);
echo 'Most voted solution: ', (microtime(true) - $time), 's', PHP_EOL;

$time = microtime(true);
this_answer_solution($elements);
echo 'This answer solution: ', (microtime(true) - $time), 's', PHP_EOL;

function accepted_solution($array){
 $dupe_array = array();
 foreach($array as $val){
  // sorry, but I had to add below line to remove millions of notices
  if(!isset($dupe_array[$val])){$dupe_array[$val]=0;}
  if(++$dupe_array[$val] > 1){
   return true;
  }
 }
 return false;
}

function most_voted_solution($array) {
   return count($array) !== count(array_unique($array));
}

function this_answer_solution(array $input_array) {
    return count($input_array) === count(array_flip($input_array));
}

Notice that accepted solution might be faster in certain condition when not unique values are near the beginning of huge array.

Upvotes: 105

Prasad Patel
Prasad Patel

Reputation: 747

One more solution from me, this is related to performance improvement

$array_count_values = array_count_values($array);
if(is_array($array_count_values) && count($array_count_values)>0)
{
   foreach ($array_count_values as $key => $value)
   {
      if($value>1)
      {
        // duplicate values found here, write code to handle duplicate values            
      }
   }
}

Upvotes: 0

Prasad Patel
Prasad Patel

Reputation: 747

To remove all the empty values from the comparison you can add array_diff()

if (count(array_unique(array_diff($array,array("")))) < count(array_diff($array,array(""))))

Reference taken from @AndreKR answer from here

Upvotes: 1

Andrew
Andrew

Reputation: 20071

$hasDuplicates = count($array) > count(array_unique($array));

Will be true if duplicates, or false if no duplicates.

Upvotes: 23

Alo
Alo

Reputation: 1

function hasDuplicate($array){
  $d = array();
  foreach($array as $elements) {
    if(!isset($d[$elements])){
      $d[$elements] = 1;
    }else{
      return true;
    } 
  } 
  return false;
}

Upvotes: -1

ะฎั€ะธะน ะกะฒะตั‚ะปะพะฒ
ะฎั€ะธะน ะกะฒะตั‚ะปะพะฒ

Reputation: 1750

The simple solution but quite faster.

$elements = array_merge(range(1,10000000),[1]);

function unique_val_inArray($arr) {
    $count = count($arr);
    foreach ($arr as $i_1 => $value) {
        for($i_2 = $i_1 + 1; $i_2 < $count; $i_2++) {
            if($arr[$i_2] === $arr[$i_1]){
                return false;
            }
        }
    }
    return true;
}

$time = microtime(true);
unique_val_inArray($elements);
echo 'This solution: ', (microtime(true) - $time), 's', PHP_EOL;

Speed - [0.71]!

Upvotes: -1

Ankita Mehta
Ankita Mehta

Reputation: 452

$duplicate = false;

 if(count(array) != count(array_unique(array))){
   $duplicate = true;
}

Upvotes: 6

Mike Sherov
Mike Sherov

Reputation: 13427

You can do: 

function has_dupes($array) {
    $dupe_array = array();
    foreach ($array as $val) {
        if (++$dupe_array[$val] > 1) {
            return true;
        }
    }
    return false;
}

Upvotes: 41

Lakhan
Lakhan

Reputation: 13216

You can do it like that way also: This will return true if unique else return false.

$nofollow = (count($modelIdArr) !== count(array_unique($modelIdArr))) ? true : false;

Upvotes: -1

Jason McCreary
Jason McCreary

Reputation: 72971

I know you are not after array_unique(). However, you will not find a magical obvious function nor will writing one be faster than making use of the native functions.

I propose:

function array_has_dupes($array) {
   // streamline per @Felix
   return count($array) !== count(array_unique($array));
}

Adjust the second parameter of array_unique() to meet your comparison needs.

Upvotes: 260

Abraham Romero
Abraham Romero

Reputation: 1117

I'm using this:

if(count($array)==count(array_count_values($array))){
    echo("all values are unique");
}else{
    echo("there's dupe values");
}

I don't know if it's the fastest but works pretty good so far

Upvotes: 0

Miles Bennet
Miles Bennet

Reputation: 17

Keep it simple, silly! ;)

Simple OR logic... 

function checkDuplicatesInArray($array){
    $duplicates=FALSE;
    foreach($array as $k=>$i){
        if(!isset($value_{$i})){
            $value_{$i}=TRUE;
        }
        else{
            $duplicates|=TRUE;          
        }
    }
    return ($duplicates);
}

Regards!

Upvotes: 0

mazgalici
mazgalici

Reputation: 606

Php has an function to count the occurrences in the array http://www.php.net/manual/en/function.array-count-values.php

Upvotes: -1

micadelli
micadelli

Reputation: 2482

Here's my take on thisโ€ฆ after some benchmarking, I found this to be the fastest method for this.

function has_duplicates( $array ) {
    return count( array_keys( array_flip( $array ) ) ) !== count( $array );
}

โ€ฆor depending on circumstances this could be marginally faster.

function has_duplicates( $array ) {
    $array = array_count_values( $array );
    rsort( $array );
    return $array[0] > 1;
}

Upvotes: 5

Muhammad Raheel
Muhammad Raheel

Reputation: 19882

Find this useful solution

function get_duplicates( $array ) {
    return array_unique( array_diff_assoc( $array, array_unique( $array ) ) );
}

After that count result if greater than 0 than duplicates else unique.

Upvotes: 1

delete me
delete me

Reputation:

As you specifically said you didn't want to use array_unique I'm going to ignore the other answers despite the fact they're probably better.

Why don't you use array_count_values() and then check if the resulting array has any value greater than 1?

Upvotes: -1

Bwmat
Bwmat

Reputation: 4578

Two ways to do it efficiently that I can think of:

  1. inserting all the values into some sort of hashtable and checking whether the value you're inserting is already in it(expected O(n) time and O(n) space)

  2. sorting the array and then checking whether adjacent cells are equal( O(nlogn) time and O(1) or O(n) space depending on the sorting algorithm)

stormdrain's solution would probably be O(n^2), as would any solution which involves scanning the array for each element searching for a duplicate

Upvotes: 0

Related Questions