How to Filter Overlapping Rows in 2D Arrays Using PHP\'s `array_diff_assoc()` Function?

Filtering Rows of a 2D Array Based on Overlapping Rows

In PHP, the array_diff_assoc() function is commonly used to determine the difference between two arrays. However, in certain scenarios involving 2D arrays, users may encounter unexpected results when attempting to filter out overlapping rows.

A user reported using array_diff_assoc() to compare two 2D arrays but noticed that the result contained common rows from both arrays instead of only the unique rows. To understand the issue, let's examine the sample data provided by the user:

$array1 = [
    [12 => 'new q sets'],
    [11 => 'common set']
];

$array2 => [
    [11 => 'common set']
];

After calling array_diff_assoc($array1, $array2), the user expected to receive an output containing only the unique row from $array1 (i.e., '[12 => 'new q sets']'). However, the actual output was:

[
    [11 => 'common set']
]

The problem lies in the way PHP compares values in array_diff_assoc(). Two values are considered equal only if they are strictly equal as strings. In the case of the 2D arrays provided, the value associated with the key '11' in both arrays is the string 'common set'. However, the key-value pairs themselves are not identical as arrays.

As a result, when array_diff_assoc() compares the two arrays, it finds that the key-value pair [11 => 'common set'] is common to both arrays and excludes it from the difference. This behavior stems from the fact that all arrays in PHP are internally represented as the string "Array".

To address this issue, one can utilize a different approach to filter out overlapping rows between 2D arrays. One common method involves creating a unique identifier for each row and using that identifier as the key for an associative array. Here's an example:

$uniqueIdentifiers = [];
$filteredRows = [];

foreach ($array1 as $row) {
    $uniqueIdentifier = implode('|', array_values($row));
    $uniqueIdentifiers[$uniqueIdentifier] = true;
}

foreach ($array2 as $row) {
    $uniqueIdentifier = implode('|', array_values($row));
    if (isset($uniqueIdentifiers[$uniqueIdentifier])) {
        unset($uniqueIdentifiers[$uniqueIdentifier]);
    }
}

foreach ($uniqueIdentifiers as $uniqueIdentifier => $isPresent) {
    $filteredRows[] = array_values(array_flip(explode('|', $uniqueIdentifier)));
}

This approach creates a unique identifier for each row by concatenating the array values and using that as the key. It then iterates through the second array and unsets any matching unique identifiers from the list. Finally, it iterates through the remaining unique identifiers, flips the keys and values to reconstruct the rows, and adds them to the $filteredRows array.

By utilizing this method, you can effectively filter out overlapping rows between 2D arrays while ensuring that unique rows are correctly identified and returned in the result.

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