PHP Append One Array to Another

By IncludeHelp Last updated : February 25, 2024

Arrays are a fundamental data structure in PHP, allowing developers to store and manipulate collections of data efficiently. One common task is appending one array to another, which simply means combining their elements into a single array. In this tutorial, we will understand various methods to append one array to another in PHP, with the help of different functions including array_merge() and array_push().

For those of you who don't know what appending is, let's understand by an example.

Imagine you have two baskets of fruits, one containing apples and the other containing oranges. Appending one array to another is like combining these two baskets into a single larger basket. So, after appending, you have a single basket with both apples and oranges, rather than keeping them separate in two different baskets.

In PHP, this can be achieved with the help of some functions. Let's have a look at each function with relevant examples.

Using array_merge() Function

The array_merge() function in PHP is a versatile function for combining two arrays into a new array.

Syntax for array_merge():

array array_merge ( array $array1 [, array $... ] )

$array1: The first array to merge.
$...: Additional arrays to merge.

Example to Append One Array to Another Using array_merge() Function

Consider a scenario where you have multiple arrays representing different categories, and you want to merge them into a single array.

<?php
$books = ["PHP Programming", "JavaScript Essentials"];
$videos = ["Introduction to Web Development", "Advanced CSS Techniques"];
$articles = ["Building Scalable Web Applications", "Best Practices for PHP Developers"];

//This line of code is used to Merge arrays representing different categories
$mergedContent = array_merge($books, $videos, $articles);

echo "Merged Content:\n";

// then we have to display the merged array using foreach loop
foreach ($mergedContent as $content) {
    echo $content . "\n";
}
?>

The output of the above example is:

Merged Content:
PHP Programming
JavaScript Essentials
Introduction to Web Development
Advanced CSS Techniques
Building Scalable Web Applications
Best Practices for PHP Developers

Explanation

The code brings together information from three different lists (books, videos, and articles) into a single list for easier handling.
It uses the array_merge function to combine these three lists into a new, unified list.
The code then shows the merged content using a loop, printing each item on a new line.
This approach simplifies managing and presenting varied data, making it more convenient to work with content from different categories.
The output reveals the successfully merged content, demonstrating how arrays help organize and streamline diverse information.

Using array_push() Function

Another approach to append one array to another is by using the array_push() method. This method allows elements of the second array to be added to the end of the first array in-place.

Syntax for array_push:

int array_push ( array &$array , mixed $... )

&$array: The array to which elements will be pushed.
$...: Elements to be pushed into the array.

Example to Append One Array to Another Using array_push() Function

Consider a use case where you have a shopping cart represented by an array, and you want to add new items to it using array_push():

<?php
$shoppingCart = ["Laptop", "Headphones"];

$newItems = ["Mouse", "External Hard Drive"];

// This line of code is used to add new items 
// to the shopping cart using array_push
array_push($shoppingCart, ...$newItems);

echo "Updated Shopping Cart:\n";

// Finally we display the modified array using foreach loop
foreach ($shoppingCart as $item) {
    echo $item . "<br>";
}
?>

The output of the above example is:

Updated Shopping Cart: Laptop
Headphones
Mouse
External Hard Drive

Explanation

We begin with a shopping cart containing a laptop and headphones.
There are new items - a mouse and an external hard drive - that we want to add to the cart
We use array_push() to add the new items to the existing shopping cart.
The code then displays the updated shopping cart with the new items.
The final output shows the modified shopping cart, now including the laptop, headphones, mouse, and external hard drive.

Array Concatenation with + (Deprecated Warning)

In older PHP versions, it was common to use the + operator for array concatenation. However, this approach is now deprecated and might trigger fatal warnings in newer PHP versions. It's advisable to avoid this method for better code compatibility.

Best Practices and Considerations

Performance Considerations

When choosing between array_merge() and array_push(), consider the performance implications. array_merge() creates a new array, which can be less efficient for large arrays. On the other hand, array_push() modifies the array in place, making it more performant for certain scenarios.

Let's consider a case where you have two arrays, array1 and array2, both containing a large number of elements. If you use array_merge() to combine these arrays, it would create a new array, consuming additional memory:

$array1 = [1, 2, 3, /* ... a large number of elements ... */];
$array2 = ['a', 'b', 'c', /* ... a large number of elements ... */];
$result = array_merge($array1, $array2);

In this example, the $result array is a new array that holds the elements of both $array1 and $array2. This can be less memory-efficient for large arrays.

Now, consider using array_push to append elements from one array to another.

$array1 = [1, 2, 3, /* ... a large number of elements ... */];
$array2 = ['a', 'b', 'c', /* ... a large number of elements ... */];
foreach ($array2 as $element) {
    array_push($array1, $element);
}

In this case, the $array1 is modified in place by adding elements from $array2. This can be more memory-efficient, especially when dealing with large datasets, as it avoids the creation of a new array.

Remember that the choice between array_merge and array_push depends on the specific use case and requirements, including the desired behaviour and performance considerations.

Type-Safe Appending

Ensure that the arrays being appended are of the same type, especially when dealing with mixed data types. Unexpected behaviour may occur if the arrays have different data types for their elements.

Let's suppose you have two arrays, one containing numbers and the other containing strings. If you try to append these arrays without converting them to a consistent data type, unexpected behaviour may occur. For instance, combining a numeric array with a string array may lead to confusion or errors, as the elements don't have a unified type.
It's essential to ensure that arrays being appended have the same data type to maintain consistency in your data and prevent unexpected outcomes.

Utilizing [] for Conciseness

In PHP 5.4 and later versions, the shorthand [] syntax can be used for array appending. It provides a concise and readable way to add elements to an array.

<?php 
$arr1 = [1, 2]; 
$arr2 = [3, 4]; 

// Append elements using []
$arr1[] = $arr2;
print_r($arr1);
?>

Conclusion

In conclusion, appending one array to another is a common operation in PHP, and developers can choose from various methods such as array_merge() and array_push(). Understanding the performance implications and adhering to best practices ensures efficient and error-free code. Additionally, the use of newer language features like the spread operator and shorthand syntax enhances code readability and conciseness. By following these guidelines, developers can effectively manage and manipulate arrays in PHP applications.

To understand the above examples, you should have the knowledge of the following PHP Topics: