Why does array_diff_assoc() return common elements instead of unique elements?

Array Filtering using array_diff_assoc()

In PHP, array_diff_assoc() is a useful function for comparing arrays and identifying differences. However, users may encounter an issue where the resulting output includes common elements instead of the expected unique elements.

To understand this, let's examine the behavior of array_diff_assoc() more closely. This function performs a strict equality comparison between key-value pairs. This means that the string representation of elements must be identical for comparison.

Consider the following example:

<code class="php">$array1 = [
    [12 => 'new q sets'],
    [11 => 'common set']
];

$array2 = [
    [11 => 'common set']
];</code>

When array_diff_assoc() is applied to these arrays, it compares the following:

Array ([0] => "Array" [1] => "Array")
Array ([0] => "Array")

Since the key-value pairs are not identical, the comparison returns the [1] element from the first array ([1] => Array( [11] => common set )). This is not the desired result, as it includes the common element.

To resolve this issue, users should ensure that the string representations of key-value pairs are identical in both arrays. This can be achieved by using consistent formatting or data types. Additionally, casting values to strings (e.g., (string) $element) can help ensure strict equality comparison.

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