A trap for mixing arrays (partially arrays, partly objects) using array_column

M66 2025-04-28

In PHP, array_column is a commonly used function that can extract the value of a column from a multidimensional array. Normally, array_column works fine when dealing with pure arrays, but using array_column may encounter some problems when elements in an array are of mixed types (i.e. part is an array, part is an object).

1. Basic usage of array_column function

The basic usage of the array_column function is as follows:

 array_column(array $input, mixed $column_key, mixed $index_key = null): array

$input : The multi-dimensional array of input.
$column_key : The key of the column that needs to be extracted (key name of the array or attribute name of the object).
$index_key : optional, used to specify the key name as the return result array.

For example, if we have a simple array:

 $data = [
    ['id' => 1, 'name' => 'Alice'],
    ['id' => 2, 'name' => 'Bob'],
    ['id' => 3, 'name' => 'Charlie']
];
$names = array_column($data, 'name');
print_r($names);

The output result will be:

 Array
(
    [0] => Alice
    [1] => Bob
    [2] => Charlie
)

2. Problems in mixed arrays

The problem can arise when we pass a mixed array to array_column , i.e. the array contains both arrays and objects. For example, suppose we have the following mixed array:

 $data = [
    ['id' => 1, 'name' => 'Alice'],
    (object)['id' => 2, 'name' => 'Bob'],
    ['id' => 3, 'name' => 'Charlie']
];

At this point, when we try to extract the name column with array_column , we encounter problems:

 $names = array_column($data, 'name');
print_r($names);

The output at this time might be:

 Array
(
    [0] => Alice
    [1] => Bob
    [2] => Charlie
)

The root of the problem

An important premise of array_column is that elements in an array should have the same structure. If the elements of an array contain both an array and an object, array_column will find the target column based on the structure of the array and the properties of the object. However, in PHP, arrays and objects are accessed differently:

The access method of arrays is through key names (such as $array['key'] ).
The access method of objects is through properties (such as $object->property ).

When an object is included in a mixed array, array_column cannot find the properties in the object uniformly, resulting in incomplete return value or throwing an error.

3. Solution

To solve this problem, we can handle mixed arrays in the following ways:

3.1 Unified array structure

The easiest way is to unify all elements into an array or object instead of mixing them. For example, convert all objects into an array:

 $data = [
    ['id' => 1, 'name' => 'Alice'],
    (object)['id' => 2, 'name' => 'Bob'],
    ['id' => 3, 'name' => 'Charlie']
];

// Convert objects to array
foreach ($data as &$item) {
    if (is_object($item)) {
        $item = (array)$item;
    }
}

$names = array_column($data, 'name');
print_r($names);

This will output correctly:

 Array
(
    [0] => Alice
    [1] => Bob
    [2] => Charlie
)

3.2 Extract object properties using custom functions

If the structure cannot be unified, you can use custom functions to handle elements of object type. For example:

 function get_name($item) {
    if (is_object($item)) {
        return $item->name;
    }
    return $item['name'];
}

$data = [
    ['id' => 1, 'name' => 'Alice'],
    (object)['id' => 2, 'name' => 'Bob'],
    ['id' => 3, 'name' => 'Charlie']
];

$names = array_map('get_name', $data);
print_r($names);

This method ensures that the name attribute can be extracted correctly regardless of whether the element is an array or an object.

4. Summary

array_column is a powerful tool, but it encounters some problems when dealing with mixed arrays, especially when array elements are combinations of arrays and objects. To avoid errors, it is best to ensure that the array element types are unified when using array_column , or to process different types of data in other ways. Through these methods, we can better utilize the array_column function to avoid problems caused by inconsistent data structures.

Hope this article helps you! If you have more questions, please continue to discuss it!

array_column