How to deal with empty arrays after merging PHP arrays?

When using array_merge() in PHP to merge arrays, containing empty strings or empty arrays will produce confusing results. Solution: 1. Use array_filter() to filter null values. 2. For cases containing empty arrays, use the recursive merge function array_merge_recursive_distinct() to maintain a consistent array structure.

Array merge when dealing with empty arrays in PHP

In PHP, use array_merge() When the function merges arrays, the end result can be confusing if one or more of the arrays contains empty elements.

Case 1: Merging arrays containing empty strings

$arr1 = [1, 2, 3];
$arr2 = [4, 5, ''];

$merged = array_merge($arr1, $arr2);

var_dump($merged);

Output:

array(6) {
  [0] => int(1)
  [1] => int(2)
  [2] => int(3)
  [3] => int(4)
  [4] => int(5)
  [5] => string(0) ""
}

As you can see, the empty strings are retained in the merge in the subsequent array.

Solution: Use array_filter() to filter null values

To remove null values ​​before merging, you can use array_filter() Function:

$arr1 = [1, 2, 3];
$arr2 = [4, 5, ''];

$arr1 = array_filter($arr1);
$arr2 = array_filter($arr2);

$merged = array_merge($arr1, $arr2);

var_dump($merged);

Output:

array(5) {
  [0] => int(1)
  [1] => int(2)
  [2] => int(3)
  [3] => int(4)
  [4] => int(5)
}

The empty string has been filtered, and the merged array does not contain empty values.

Case 2: Merge of arrays containing empty arrays

If the array contains empty arrays, a multidimensional array may be unexpectedly produced after merging:

$arr1 = [1, 2, 3];
$arr2 = [4, 5, []];

$merged = array_merge($arr1, $arr2);

var_dump($merged);

Output:

array(6) {
  [0] => int(1)
  [1] => int(2)
  [2] => int(3)
  [3] => int(4)
  [4] => int(5)
  [5] => array(0) {
  }
}

The empty array constitutes one element in the merged array, causing the result to be a multidimensional array.

Solution: Use recursive merging

To solve this problem, you can use the recursive merging method, which treats empty arrays as ordinary elements for merging:

function array_merge_recursive_distinct(array &$array1, array &$array2)
{
    $merged = $array1;

    foreach ($array2 as $key => &$value) {
        if (is_array($value) && isset($merged[$key]) && is_array($merged[$key])) {
            $merged[$key] = array_merge_recursive_distinct($merged[$key], $value);
        } else {
            $merged[$key] = $value;
        }
    }

    return $merged;
}

$arr1 = [1, 2, 3];
$arr2 = [4, 5, []];

$merged = array_merge_recursive_distinct($arr1, $arr2);

var_dump($merged);

Output:

array(6) {
  [0] => int(1)
  [1] => int(2)
  [2] => int(3)
  [3] => int(4)
  [4] => int(5)
  [5] => NULL
}

The empty array has been converted to NULL, and the merged array structure remains consistent.

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