How to Determine the Difference Between Object Arrays by Comparing Specific Property Values?

Determining the Difference Between Two Arrays of Objects by Comparing Specific Property Values

Question:

Legacy functions such as array_diff and array_udiff are designed for comparing arrays of scalar values. How can we determine the difference between two arrays of objects, where we want to compare based on a specific property value?

Solution:

Fortunately, array_udiff can be leveraged to address this requirement. We define a custom comparison function that focuses on the desired property, and then utilize array_udiff to determine the difference between the two arrays.

Consider the following example arrays:

<code class="php">$array1 = array(
    (object) ['id' => '205', 'day_id' => '12'],
    ...
);

$array2 = array(
    (object) ['id' => '205', 'day_id' => '13'],
    ...
);</code>

Our goal is to identify the differences between these arrays based on the id property. To achieve this, we can create a comparison function:

<code class="php">function compare_objects($obj_a, $obj_b) {
  return $obj_a->id - $obj_b->id;
}</code>

This function compares the id property of two objects and returns the difference as an integer. We then utilize array_udiff as follows:

<code class="php">$diff = array_udiff($array1, $array2, 'compare_objects');</code>

Alternatively, with PHP 5.3 and above, we can employ an anonymous function for comparison:

<code class="php">$diff = array_udiff($array1, $array2,
  function ($obj_a, $obj_b) {
    return $obj_a->id - $obj_b->id;
  }
);</code>

This solution effectively calculates the difference between two arrays of objects by comparing the specified property value. The resulting $diff array will contain objects representing the unique elements from either $array1 or $array2 based on the comparison criteria.

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