php: check if an array has duplicates

Question

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.

Answer 1

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

Answer 2

Here's my take on this… 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 );
}

…or depending on circumstances this could be marginally faster.

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

Answer 3

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?

Answer 4

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;

Answer 5

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.

Answer 6

⚡ PERFORMANCE 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.

As said in manual array keys can be only type of int or string so this is what you can have in original array values to compare, otherwise PHP will start casting with unexpected results.

PROOF FOR 10M RECORDS ARRAY

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