To merge two PHP arrays and keep unique values, there are two main methods. 1. For index arrays or only deduplication, use array_merge and array_unique combinations: first merge array_merge($array1, $array2) and then use array_unique() to deduplicate them to finally get a new array containing all unique values; 2. For associative arrays and want to retain key-value pairs in the first array, use the operator: $result = $array1 $array2, which will ensure that the keys in the first array will not be overwritten by the second array. These two methods are suitable for different scenarios, and are selected based on whether the key names need to be retained or only the uniqueness of the value is focused on.

Sometimes we need to merge two PHP arrays and only retain unique values. This is common when dealing with data deduplication, filtering, or integrating data from multiple sources. In fact, the method is not complicated, just use the right function.

Use array_merge and array_unique to deduplicate

This is the most commonly used method: first merge the array, then remove the heavy. The steps are as follows:

• Use array_merge($array1, $array2) to combine two arrays into one
• Use array_unique() to remove duplicate values

 $array1 = [1, 2, 3];
$array2 = [3, 4, 5];

$result = array_unique(array_merge($array1, $array2));

In this way, $result will be [1, 2, 3, 4, 5] . Note that if there are strings or other types of data in the array, this method also applies. Moreover, it can also handle the situation of index arrays and associative arrays. However, when using array_merge in associative arrays, the subsequent array will be retained if the value of the same key name is the same.

If it is an associative array, consider using Operators

If you have two associative arrays (that is, the kind that uses strings as key names) and want to keep the values ??in the first array and only add the items in the second array that do not exist in the first one, you can write this:

 $array1 = ['a' => 1, 'b' => 2];
$array2 = ['b' => 3, 'c' => 4];

$result = $array1 $array2;

The result will be:

 ['a' => 1, 'b' => 2, 'c' => 4]

As you can see, 'b' => 3 in $array2 is ignored because $array1 already has the 'b' key. This method is suitable for you to only want to keep the key-value pairs already in the first array, while completing the part of the second array that has no conflicts.

For PHP 7.4, can I use the array_union function?

Actually not. PHP does not have a built-in array_union function. But some developers will encapsulate a function similar to the function to simulate this behavior. for example:

 function array_union($a, $b) {
    return $a $b;
}

However, this only applies to associative arrays. For index arrays, it is more safe to recommend the aforementioned array_merge array_unique method.

Basically that's it. When choosing different combination methods in different scenarios, the key depends on whether you want to keep the key names first or only care about the uniqueness of the value.

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