Get Unique Elements from Two Arrays in PHP

1. Basic Method (Preserves Types)

$array1 = [5, 12];
$array2 = ["18", "12"];
$merged = array_merge($array1, $array2);
$unique = array_unique($merged);

$array1 = [5, 12];

$array2 = ["18", "12"];

$merged = array_merge($array1, $array2);

$unique = array_unique($merged);

This is the simplest approach but maintains type differences. The number 12 and string “12” will be treated as distinct values.

Result: [5, 12, “18”, “12”] (keeps both 12 and “12”)

2. Type-Unified Method (Converts all to strings)

$unique = array_unique(array_map('strval', array_merge($array1, $array2)));

1	$unique = array_unique(array_map('strval', array_merge($array1, $array2)));

Converts all values to strings first, which ensures “12” and 12 become the same value. Useful when type differences don’t matter.

Result: [“5”, “12”, “18”] (all values as strings)

3. Numeric Method (Converts all to numbers)

$unique = array_unique(array_map('intval', array_merge($array1, $array2)));

1	$unique = array_unique(array_map('intval', array_merge($array1, $array2)));

Converts all values to integers, which is useful when you’re working with numeric data and want to ignore string/integer type differences.

Result: [5, 12, 18] (all values as integers)

4. Using array_diff with array_merge

$merged = array_merge($array1, $array2);
$unique = array_keys(array_flip($merged));

1 2	$merged = array_merge($array1, $array2); $unique = array_keys(array_flip($merged));

This clever technique uses array_flip() which automatically removes duplicate values since array keys must be unique. Then we extract the keys back to values.

Note: This is one of the fastest methods for large arrays but reindexes the array.

5. Using the + Operator (Union)

$unique = $array1 + $array2;

1	$unique = $array1 + $array2;

The union operator (+) merges arrays but only works properly for associative arrays with unique keys. Not recommended for indexed arrays like in our example.

Warning: For numeric arrays, this method doesn’t work as expected for merging values.

6. Custom Function with array_reduce

$unique = array_reduce(array_merge($array1, $array2), 
function($carry, $item) {
if (!in_array($item, $carry, true)) {
$carry[] = $item;
}
return $carry;
}, []);

$unique = array_reduce(array_merge($array1, $array2),

function($carry, $item) {

if (!in_array($item, $carry, true)) {

$carry[] = $item;

}

return $carry;

}, []);

This method provides complete control over the comparison process. The true parameter in in_array() ensures strict type comparison.

Advantage: You can customize the comparison logic as needed.

7. Using array_flip Twice

$unique = array_flip(array_flip(array_merge($array1, $array2)));

1	$unique = array_flip(array_flip(array_merge($array1, $array2)));

Similar to method 4, this exploits the fact that array keys must be unique. Flipping twice removes duplicates while preserving the last occurrence of each value.

Performance: This is very fast for large arrays but converts values to strings during the flip operation.

Recommendations

For small arrays where type matters: Use Method 1 (basic array_unique)
For numeric data: Use Method 3 (convert to int)
For large arrays: Use Method 4 or 7 (array_flip techniques)
When you need custom comparison logic: Use Method 6 (array_reduce)

PHP Tutorial