When working with PHP, it's not uncommon to come across situations where you have two or more arrays that you need to combine into a single, unified array. This could happen, for example, when you're querying a database and want to combine the results of multiple queries into one array, or when you want to merge in some default values from one array with some user input from another array.

There are several ways to combine arrays in PHP, but one of the most commonly used ways is with the `array_merge` function. In this article, we'll take a closer look at `array_merge` and how it can simplify your PHP code and increase efficiency.

What is array_merge?

The `array_merge` function is a built-in PHP function that takes two or more arrays as arguments and returns a new array that contains all the elements from those arrays. It's similar to the `+` operator for arrays, but with an important difference: `array_merge` will keep both numeric and string keys, whereas the `+` operator will only keep the keys from the first array.

Here's an example to illustrate the difference:

```

$a = array('a' => 1, 'b' => 2);

$b = array('b' => 3, 'c' => 4);

echo implode(', ', $a + $b); // Output: 1, 2

$result = array_merge($a, $b);

echo implode(', ', $result); // Output: 1, 2, 3, 4

```

In the first example, we're using the `+` operator to combine `$a` and `$b`. As you can see, only the keys from the first array (`$a`) are kept, so the output only includes the values `1` and `2`. In the second example, we're using `array_merge` instead, which combines all the elements from both arrays, resulting in an output of `1, 2, 3, 4`.

Using array_merge to simplify your PHP code

One of the biggest advantages of using `array_merge` instead of other array combination methods is that it can help simplify your PHP code. Here's an example:

```

// Without array_merge

$default = array(

'name' => '',

'email' => '',

'phone' => '',

);

$user_input = array(

'name' => 'John Smith',

'email' => 'john@example.com',

);

$values = $user_input + $default;

// With array_merge

$default = array(

'name' => '',

'email' => '',

'phone' => '',

);

$user_input = array(

'name' => 'John Smith',

'email' => 'john@example.com',

);

$values = array_merge($default, $user_input);

```

In the first example, we're combining the `$user_input` array with the `$default` array using the `+` operator. This works, but it's not very intuitive and can be difficult to read and understand. In the second example, we're using `array_merge` instead, which is a much more clear and concise way to combine arrays.

Using array_merge to increase efficiency

Another advantage of using `array_merge` is that it can help increase the efficiency of your PHP code. In some cases, using `array_merge` instead of other methods of array combination can result in faster code execution.

Here's an example that shows how `array_merge` can be more efficient:

```

// Without array_merge

$merged = $array1;

foreach ($array2 as $key => $value) {

if (isset($merged[$key])) {

if (is_array($value)) {

$merged[$key] = array_merge($merged[$key], $value);

} else {

$merged[$key] = $value;

}

} else {

$merged[$key] = $value;

}

}

// With array_merge

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

```

In the first example, we're combining `$array1` and `$array2` using a foreach loop that checks each key in `$array2` to see if it already exists in `$array1`. If it does, we use `array_merge` to combine the two arrays. If it doesn't, we simply add the key to `$merged`. This works, but it can be slow and inefficient, especially for large arrays.

In the second example, we're using `array_merge` instead, which is a much more efficient way to combine arrays. `array_merge` is a built-in function that's optimized for array concatenation, so it can often be faster and more efficient than other methods.

Conclusion

Combining arrays is a common task in PHP development, and there are several ways to do it. However, `array_merge` is one of the most powerful and versatile methods available. With `array_merge`, you can combine arrays in a simple and intuitive way, and it can often result in more efficient code execution. By taking advantage of this powerful PHP function, you can simplify your code, increase efficiency, and save time and resources in your PHP development projects.