php - Copy value from array into another array in multidimensional array

Question

I have an array that contains multiple transactions, with multiple transactions being from the same email address.

Some of these transactions have a value in the client key. Others don't.

I want to copy the filled client key in all matching arrays with the same email_address key, in order to always have data in the client key.

Example of my array:

Array
(
    [1] => Array
        (
            [client] => John John
            [email_address] => [email protected]
        )

    [3] => Array
        (
            [client] => Kevin Kevin
            [email_address] => [email protected]
        )

    [5] => Array
        (
            [client] => 
            [email_address] => [email protected]
        )

)

What I want to achieve is to make sure that Array [5] has the same value in the client key as Array [1] because it's the same client (based on email_address key).

Example of the resulted array:

Array
(
    [1] => Array
        (
            [client] => John John
            [email_address] => [email protected]
        )

    [3] => Array
        (
            [client] => Kevin Kevin
            [email_address] => [email protected]
        )

    [5] => Array
        (
            [client] => John John
            [email_address] => [email protected]
        )

)

How can I go through the array to make sure that matching arrays (based on email_address key) always have the same client key?

Answer 1

The solution using array_column, array_unique, array_flip, array_count_values, array_filter and array_intersect_key functions (This solution is also well-suited for processing multiple groups of "client" entries with same "email_address"):

// supposing $arr is your initial array

$ties = array_flip(array_unique(array_column($arr, "email_address", "client")));
$counts = array_filter(array_count_values(array_column($arr, "email_address")), function($v){
    return $v > 1;  // getting number of entries with same 'email' attribute
});    
$relations = array_intersect_key($ties, $counts);   // contains pairs of relative email/client entries, like "[[email protected]] => John John"

foreach ($arr as &$client) {
    if (!$client['client'] && key_exists($client['email_address'], $relations)) {
        $client['client'] = $relations[$client['email_address']];
    }
}

print_r($arr);

The output:

Array
(
    [1] => Array
        (
            [client] => John John
            [email_address] => [email protected]
        )

    [3] => Array
        (
            [client] => Kevin Kevin
            [email_address] => [email protected]
        )

    [5] => Array
        (
            [client] => John John
            [email_address] => [email protected]
        )
)

Answer 2

You can make an intermediate array that relates email addresses to client. Like this:

$intermediateArray = [];

foreach ($inputArray as $row) {
  if (isset($row['client']) {
    $intermediateArray[$row['email_address']] = $row['client']
  }
}

and then fill in the missing client cells:

foreach ($inputArray as $row) {
  if (!isset($row['client']) {
    if (isset($intermediateArray[$row['email_address']])) {
      $row['client'] = $intermediateArray[$row['email_address']];
    }   
  }
}

More efficient solutions are possible, but this one seems the simplest.