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PHP array_diff() Function

Quick summary: The PHP array_diff() function computes the difference of arrays using values only.

PHP array_diff() Syntax 

array_diff(array $array, array ...$arrays): array
PHP

PHP array_diff() Basic examples 

var_dump(array_diff([1,2,3], [2]));
PHP
Output:
array(2) {
  [0]=> int(1)
  [2]=> int(3)
}

Returns values present in the first array but not in the second.

PHP array_diff() Real-world usage 

$allowed = ['read','write'];
$requested = ['read','delete'];
var_dump(array_diff($requested, $allowed));
PHP
Output:
array(1) {
  [1]=> string(6) "delete"
}

Detects unsupported permissions.

PHP array_diff() Edge cases 

var_dump(array_diff(["1", 1], [1]));
PHP
Output:
array(0) {
}

Comparison is non-strict and values are considered equal.

PHP array_diff() Common mistakes

Expecting key comparison

array_diff compares values only.

Incorrect
array_diff(['a'=>1], ['b'=>1]);
Correct
array_diff_assoc(['a'=>1], ['b'=>1]);

Use array_diff_assoc for key comparison.

PHP array_diff() Frequently Asked Questions

What does array_diff() do in PHP?

array_diff() returns the values from the first array that are not present in any of the other arrays.

What is the syntax of array_diff()?

array_diff(array $array, array ...$arrays): array

Does array_diff() preserve array keys?

Yes, array_diff() preserves the keys from the first array.

Is array_diff() case-sensitive?

Yes, comparisons are case-sensitive by default.

Does array_diff() compare keys or values?

array_diff() compares only values, not keys.

What happens with duplicate values in array_diff()?

All matching values found in other arrays are removed, including duplicates.

Can array_diff() work with multiple arrays?

Yes, you can pass multiple arrays to compare against.

Does array_diff() modify the original array?

No, it returns a new array without modifying the original.

What is the difference between array_diff() and array_diff_assoc()?

array_diff() compares only values, while array_diff_assoc() compares both keys and values.

Can array_diff() be used with associative arrays?

Yes, but only values are compared; keys are ignored.

What is a real-world use case of array_diff()?

Finding missing items, filtering datasets, or comparing lists.

Can array_diff() be combined with other functions?

Yes, it is often used with array_intersect() or array_filter() for data processing.

PHP array_diff() Related PHP Functions