


How to Filter Rows from a 2D Array Based on Intersection with Another 2D Array in PHP?
Oct 26, 2024 am 06:24 AMFiltering Rows of a 2D Array Based on Row Intersections
In PHP, the array_diff_assoc() function is designed to find the difference between two arrays while prioritizing key-value pairs. However, while using this function to filter rows from a 2D array based on intersection with another 2D array, it may not always yield the expected results.
Understanding the Issue
The problem arises due to the strict comparison performed by array_diff_assoc(). It compares string representations of key-value pairs during comparison. This means that even if two key-value pairs contain the same values, they are not considered equal unless their string representations are identical.
Sample Data
Consider the following sample data:
<code class="php">$array1 = [ [12 => 'new q sets'], [11 => 'common set'] ]; $array2 = [ [11 => 'common set'] ];</code>
Incorrect Output
When we attempt to use array_diff_assoc() to filter $array1 based on the rows in $array2, we get an incorrect output:
<code class="php">$output = array_diff_assoc($array1, $array2); print_r($output); // Output: [ // [11 => 'common set'] // ]</code>
This output shows that the common row is present in the result, while the intended output should contain the exclusive row from $array1.
Cause of the Issue
As mentioned earlier, the problem lies in the strict comparison performed by array_diff_assoc(). When comparing the following two arrays:
<code class="php">Array ( [0] => "Array" [1] => "Array" ) Array ( [0] => "Array" )</code>
the function returns the different key-value pair as the result because the key-value pairs are not string-identical.
Correct Approach
To address this issue, we can use a slightly different approach that checks for the existence of specific key-values in the arrays:
<code class="php">$filteredRows = array_filter($array1, function($row) use ($array2) { return !in_array($row, $array2); }); print_r($filteredRows); // Output: [ // [12 => 'new q sets'] // ]</code>
This approach uses in_array() to check if each row from $array1 is present in $array2. If a row is not present in $array2, it is included in the filtered results.
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