PHP array_intersect + array_flip with array that has values multiple times

Question

I have two arrays:

$arr1 = array(101 => 250, 102 => 250, 103 => 250, 104 => 500, 105 => 500, 106 => 500,);

and

Answer 1

Using the standard php library functions for this might reduce the readability of the code. I would go with an explicit foreach loop that goes over $arr2.

$ans = array();

foreach($arr2 as $key) {
    if (isset($arr1[$key]) && !in_array($arr1[$key], $ans)) {
        $ans[$key] = $arr1[$key];
    }
}

This function should O(n*n) where n is the length of $arr2.

Answer 2

The following code does the job. I hope it is self-explanatory.

array_unique(array_intersect_key($arr1, array_flip($arr2)))