Find the Non-Repeating Elements in an Array

Question

My array is :

$array= array(4,3,4,3,1,2,1);

And I\'d like to output it like below:

Output = 2 

(As 2 i

Answer 1

One-liner with no loops: (Demo)

var_export(array_keys(array_intersect(array_count_values($array),[1])));

The breakdown:

array_keys(                          // return the remaining keys from array_count_values 
    array_intersect(                 // filter the first array by second
        array_count_values($array),  // count number of occurrences of each value
        [1]                          // identify the number of occurrences to keep
    )
)

if you (or any future reader) wants to keep more values, replace the second parameter/array in array_intersect(). for instance: you want to keep 1,2,and 3: array(1,2,3) or [1,2,3]

p.s. For the record, you can use array_filter() with a custom function to omit all non-1 count values, but I have used array_intersect() because the syntax is more brief and IMO easier to read.

---

p.s. thought I'd revisit and include a PHP7.4 technique and compare against other function-based techniques...

Code: (Demo)

$numbers = [4, 3, 4, 3, 1, 2, 1];
var_export(
    array_keys(
        array_intersect(
            array_count_values($numbers),
            [1]
        )
    )
);

echo "\n---\n";
var_export(
    array_keys(
        array_filter(
            array_count_values($numbers),
            function($count) {
                return $count === 1;
            }
        )
    )
);

echo "\n---\n";
// PHP7.4+
var_export(
    array_keys(
        array_filter(
            array_count_values($numbers),
            fn($count) => $count === 1
        )
    )
);