What are some best practices for handling arrays in PHP, especially when dealing with form data and session variables?

When handling arrays in PHP, especially when dealing with form data and session variables, it's important to properly sanitize and validate the input to prevent security vulnerabilities such as SQL injection or cross-site scripting attacks. Additionally, it's good practice to use built-in PHP functions like filter_input_array() and filter_var_array() to filter and validate input data. Lastly, always remember to properly escape output data to prevent injection attacks. 

// Example of sanitizing form data using filter_input_array()

// Define an array of expected input fields
$expected_fields = array(
    'username' => FILTER_SANITIZE_STRING,
    'email' => FILTER_VALIDATE_EMAIL,
    'age' => FILTER_VALIDATE_INT
);

// Sanitize input data
$input_data = filter_input_array(INPUT_POST, $expected_fields);

// Access sanitized data
$username = $input_data['username'];
$email = $input_data['email'];
$age = $input_data['age'];

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