Common methods of traversing arrays by PHP include: 1. Use foreach to handle associative and index arrays, suitable for scenarios where indexes are not manually controlled; 2. Use for loops to traverse index arrays, suitable for situations where indexes need to be precisely controlled, but attention should be paid to avoid repeated calls to count() and non-continuous indexes; 3. While combined with each() for old versions of PHP traversal, but it has been deprecated in PHP8; 4.array_map is used to execute functions on each element and return a new array; 5.array_walk is used to directly modify the original array or execute side effects. Choosing the appropriate method according to the specific scenario can improve development efficiency and code readability.

Traversing PHP arrays is a very common operation in development. Whether you are processing form data, obtaining results from a database, or building complex logical processes, array traversal will be used. Mastering several commonly used methods can allow you to process data more flexibly in different scenarios.

Use foreach to traverse associative and index arrays

This is the most commonly used and intuitive way, especially suitable for situations where you don't need to manually control the index.

 $fruits = ['apple', 'banana', 'cherry'];

foreach ($fruits as $fruit) {
    echo "The fruit is: $fruit <br>";
}

If you have an associative array with keys, for example:

 $user = [
    'name' => 'Tom',
    'age' => 25,
    'email' => 'tom@example.com'
];

foreach ($user as $key => $value) {
    echo "$key: $value <br>";
}

This allows you to get keys and values ??at the same time, which is very suitable for displaying or processing structured data such as configuration items and user information.

Use for loop to traverse index array

If you are sure that the array is numeric indexed and need more precise control of the loop process, you can use for :

 $colors = ['red', 'green', 'blue'];
for ($i = 0; $i < count($colors); $i ) {
    echo "Colors are: " . $colors[$i] . "<br>";
}

This method is suitable for situations where you need to make specific judgments or operations based on the index, such as performing an action every other element.

But note:

• To avoid calling count() every time the loop, you can assign values ??to the variable in advance;
• If the array is not a continuous index (such as having a jump or being unset), problems may occur.

Use while and each() to traverse (old version method)

PHP 7 and previous versions support traversing arrays through each() combined with list() :

 $numbers = [10, 20, 30];
reset($numbers); // Reset the pointer to the beginning while (list($key, $value) = each($numbers)) {
    echo "The key is: $key, the value is: $value <br>";
}

However, this method has been deprecated in PHP 8, so it is not recommended to use new projects, but if you see similar writing when maintaining old code, just know what it does.

Other tips: Combined array_map or array_walk

If you want to execute a function on each element in an array, consider these functions:

• array_map() : works for you want to pass each element into the function and return a new array.
• array_walk() : works for you want to directly modify the original array or perform certain side effects (such as output).

example:

 $prices = [10.99, 20.5, 30.75];

$discounted = array_map(function($price) {
    return $price * 0.9; // 10% off}, $prices);

print_r($discounted);

This type of method is more suitable for functional style processing and has clear logic, but if you just want to print or simply process it, foreach may be more intuitive.

Basically these commonly used methods. Choose the right tool for different situations, and don’t need to memorize it by rote. Just understand the scenarios that apply to each method.

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