How do I combine two associative arrays in PHP?

Combining Associative Arrays in PHP

In PHP, combining two associative arrays into one can be achieved efficiently using the array_merge() function. Here's how you can do it:

Consider the following two associative arrays:

<code class="php">$array1 = ["name1" => "id1"];

$array2 = ["name2" => "id2", "name3" => "id3"];</code>

Method 1: array_merge()

To merge the arrays, use the array_merge() function as follows:

<code class="php">$array3 = array_merge($array1, $array2);</code>

This will create a new array $array3 that contains all the key-value pairs from both $array1 and $array2. The values for duplicate keys will be overwritten with the values from the second array.

Method 2: Array Addition ( ) Operator

Alternatively, you can use the array addition ( ) operator to merge the arrays:

<code class="php">$array4 = $array1 + $array2;</code>

This operator also merges the arrays, but it does not overwrite duplicate key values. Instead, it will result in a multidimensional array with duplicate keys.

Result

In both cases, $array3 and $array4 will be:

array(4) {
  ["name1"] => "id1",
  ["name2"] => "id2",
  ["name3"] => "id3"
}

Unit Testing

To unit test this functionality, you can create test cases that assert the expected behavior of the array_merge() function or the array addition operator. Here's an example test using PHPUnit:

<code class="php">class ArrayMergeTest extends PHPUnit_Framework_TestCase
{
    public function testArrayMerge()
    {
        $array1 = ["name1" => "id1"];
        $array2 = ["name2" => "id2", "name3" => "id3"];
        $expectedArray = ["name1" => "id1", "name2" => "id2", "name3" => "id3"];

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

        $this->assertEquals($expectedArray, $actualArray);
    }
}</code>

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