The array_replace() function in PHP is used to replace the values of the first array with the values from subsequent arrays based on their keys. If a key from the first array exists in one of the subsequent arrays, the value from that subsequent array will overwrite the value in the first array.

Syntax:

array_replace(array $array, array ...$replacements): array

Parameters:

• $array: The input array whose values will be replaced.
• $replacements: One or more arrays that provide the values to replace in the first array.

Return Value:

• Returns an array with the values from the first array replaced by the values from the subsequent arrays. The keys from the first array are preserved.

Example 1: Basic Replacement

In this example, we demonstrate how to use array_replace() to replace specific values in an array.

<?php
$array1 = ["a" => "apple", "b" => "banana", "c" => "cherry"];
$array2 = ["b" => "blueberry", "c" => "cranberry"];
$result = array_replace($array1, $array2);

print_r($result);
?>

Output:

Array
(
    [a] => apple
    [b] => blueberry
    [c] => cranberry
)

In this case, the values for keys b and c in $array1 are replaced with the corresponding values from $array2.

Example 2: Multiple Replacement Arrays

You can use array_replace() with multiple replacement arrays. The function processes the replacements from left to right.

<?php
$array1 = ["a" => "apple", "b" => "banana", "c" => "cherry"];
$array2 = ["b" => "blueberry"];
$array3 = ["c" => "cranberry", "d" => "date"];
$result = array_replace($array1, $array2, $array3);

print_r($result);
?>

Output:

Array
(
    [a] => apple
    [b] => blueberry
    [c] => cranberry
    [d] => date
)

Here, the value for b is replaced by blueberry, the value for c is replaced by cranberry, and the new key d with the value date is added.

Example 3: Key Preservation

The keys from the original array are preserved even when replaced.

<?php
$array1 = [0 => "zero", 1 => "one", 2 => "two"];
$array2 = [1 => "uno", 3 => "tres"];
$result = array_replace($array1, $array2);

print_r($result);
?>

Output:

Array
(
    [0] => zero
    [1] => uno
    [2] => two
    [3] => tres
)

In this example, the value for key 1 in $array1 is replaced by "uno" from $array2, and a new key 3 with the value "tres" is added.

Example 4: Handling Non-Existent Keys

If a key from the replacement arrays does not exist in the first array, it is simply added to the result.

<?php
$array1 = ["x" => "X-ray", "y" => "Yankee"];
$array2 = ["z" => "Zulu"];
$result = array_replace($array1, $array2);

print_r($result);
?>

Output:

Array
(
    [x] => X-ray
    [y] => Yankee
    [z] => Zulu
)

Practical Usage:

• array_replace() is useful for:
  • Merging configurations where default values may be overwritten by user-defined values.
  • Updating specific entries in a dataset while keeping others intact.
  • Constructing complex arrays from simpler parts while maintaining key-value associations.

Summary:

• array_replace($array, $replacements...) replaces the values of the first array with those from subsequent arrays based on matching keys.
• The function preserves the keys from the original array and returns a new array with the replacements applied.
• It is a flexible tool for managing and updating arrays in PHP, particularly when dealing with associative arrays.