PHP array_diff_assoc Function

last modified March 13, 2025

The PHP array_diff_assoc function compares arrays and returns differences with key checks. It's useful for finding mismatches in both keys and values.

Basic Definition

The array_diff_assoc function compares arrays and returns differences. It checks both keys and values, unlike array_diff.

Syntax: array_diff_assoc(array $array1, array $array2, ...): array. It returns elements from $array1 not present in other arrays. Comparison is strict (===).

Basic array_diff_assoc Example

This shows simple comparison of two arrays with both key and value checks.

basic_array_diff_assoc.php

<?php

$array1 = ["a" => "apple", "b" => "banana", "c" => "cherry"];
$array2 = ["a" => "apple", "b" => "blueberry", "c" => "cherry"];

$result = array_diff_assoc($array1, $array2);

print_r($result);

This compares two arrays and finds differences. The output will be: Array ( [b] => banana ) because the "b" key has different values in both arrays.

Comparing Multiple Arrays

array_diff_assoc can compare more than two arrays at once.

multiple_arrays.php

<?php

$array1 = ["a" => "apple", "b" => "banana", "c" => "cherry"];
$array2 = ["a" => "apple", "b" => "banana"];
$array3 = ["a" => "apple", "c" => "cherry"];

$result = array_diff_assoc($array1, $array2, $array3);

print_r($result);

This compares three arrays. The output will be empty because all elements in $array1 exist in at least one of the other arrays with same keys/values.

Numeric Key Comparison

The function works with numeric keys just like with string keys.

numeric_keys.php

<?php

$array1 = [1 => "one", 2 => "two", 3 => "three"];
$array2 = [1 => "one", 2 => "TWO", 4 => "four"];

$result = array_diff_assoc($array1, $array2);

print_r($result);

This compares arrays with numeric keys. The output will be: Array ( [2] => two [3] => three ) because key 2 has different values and key 3 doesn't exist in $array2.

Type-Sensitive Comparison

array_diff_assoc uses strict comparison (===) for both keys and values.

type_sensitive.php

<?php

$array1 = ["a" => "1", "b" => 2, "c" => 3.0];
$array2 = ["a" => 1, "b" => 2, "c" => 3];

$result = array_diff_assoc($array1, $array2);

print_r($result);

This demonstrates strict comparison. The output will be: Array ( [a] => 1 [c] => 3.0 ) because "1" (string) !== 1 (int) and 3.0 (float) !== 3 (int).

Complex Array Comparison

The function can handle complex arrays with nested structures.

complex_arrays.php

<?php

$array1 = [
    "fruit" => ["a" => "apple", "b" => "banana"],
    "color" => "red"
];
$array2 = [
    "fruit" => ["a" => "apple", "b" => "blueberry"],
    "color" => "red"
];

$result = array_diff_assoc($array1, $array2);

print_r($result);

This compares multidimensional arrays. The output will be empty because the function doesn't recursively compare nested arrays. Only top-level differences are detected.

Best Practices

Key Importance: Use when key-value pairs must match exactly.
Performance: Be mindful with large arrays as it's O(n*m).
Type Safety: Remember it uses strict comparison.
Nested Arrays: Combine with array_diff for deep comparison.

Source

PHP array_diff_assoc Documentation

This tutorial covered the PHP array_diff_assoc function with practical examples showing its usage for array comparison scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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