比较两个数组，并以一个特定的值（php）查找所有重复项

Question

I have two arrays, first as old, second as new. I want compare both of them and output only duplicates.

I try somethings with a pain : array_intersect and array_search without any results...

First array (old) contains as output :

[0] => Array (
    [id] => old_id_1
    [color] => red
 )

[1] => Array (
    [id] => old_id_2
    [color] => blue
 )

[2] => Array (
    [id] => old_id_3
    [color] => green
 )

[3] => Array (
    [id] => old_id_4
    [color] => purple
 )

[4] => Array (
    [id] => old_id_5
    [color] => yellow
 )

The second (new), output :

[0] => Array (
    [id] => new_id_1
    [color] => blue
)


[1] => Array (
    [id] => new_id_2
    [color] => pink
)


[2] => Array (
    [id] => new_id_3
    [color] => purple
)

As return, i want make something like :

We find 2 duplicates colors :
-  blue (new_id_1) in old_id_2 
-  purple (new_id_3) in old_id_4

If anyone have some ideas.

Answer 1

Try this:

$firstArr  = [
    ['id' => 'old_id_1', 'color' => 'red'],
    ['id' => 'old_id_2', 'color' => 'blue'],
    ['id' => 'old_id_3', 'color' => 'green'],
    ['id' => 'old_id_4', 'color' => 'purple'],
    ['id' => 'old_id_5', 'color' => 'yellow'],
];
$secondArr = [
    ['id' => 'new_id_1', 'color' => 'blue'],
    ['id' => 'new_id_2', 'color' => 'pink'],
    ['id' => 'new_id_3', 'color' => 'purple'],
];

$firstArrAssoc = array_combine(array_column($firstArr, 'color'), array_column($firstArr, 'id'));
$duplicatesArr = [];
foreach ($secondArr as $row) {
    if (array_key_exists($row['color'], $firstArrAssoc)) {
        $duplicatesArr[] = "-  $row[color] ($row[id]) in {$firstArrAssoc[$row['color']]}";
    }
}
echo "We find " . count($duplicatesArr) . " duplicates colors :\n";
echo implode("\n", $duplicatesArr);

Output:

We find 2 duplicates colors :
-  blue (new_id_1) in old_id_2
-  purple (new_id_3) in old_id_4

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