How to initialize multidimensional associative array with empty values

Question

I want to create and initialize a multidimensional array with known possible keys for the second dimension but no values.

This array will store event_ids (populated dynamically) and for each event_id an array having exactly four different counts (also filled dynamically).

Structure I want to create

Array
(
    [0] => Array  =================> This index will be the event_id 
        (
            [invitation_not_sent_count] => 
            [no_response_yet_count] => 
            [will_not_attend_count] => 
            [will_attend_count] => 
        )
)

What I did so far?

$DataArray = array();
$DataArray[] = array('invitation_not_sent_count' => '',
                                        'no_response_yet_count' => '',
                                        'will_not_attend_count' => '',
                                        'will_attend_count' => '');

And inside the loop I am populating data dynamically like:

$DataArray[$result->getId()]['no_response_yet_count'] = $NRCount;

What I get is:

Array
(
[0] => Array
    (
        [invitation_not_sent_count] => 
        [no_response_yet_count] => 
        [will_not_attend_count] => 
        [will_attend_count] => 
    )

[18569] => Array
    (
        [no_response_yet_count] => 2
    )

[18571] => Array
    (
        [no_response_yet_count] => 1
    )

)

What I want is that if a value is not available in the iteration, its entry should be empty as defined at initialization time. So if all other counts are empty in the data except no_response_yet_count , the array should be:

Expected Output

Array
(
[18569] => Array
    (
        [invitation_not_sent_count] => 
        [no_response_yet_count] => 2
        [will_not_attend_count] => 
        [will_attend_count] =>
    )

[18571] => Array
    (
        [invitation_not_sent_count] => 
        [no_response_yet_count] => 1
        [will_not_attend_count] => 
        [will_attend_count] =>
    )

)

Answer 1

I usually resort to a mapping function at that point:

function pre_map(&$row) {
    $row = array
    (
        'invitation_not_sent_count' => '',
        'no_response_yet_count' => '',
        'will_not_attend_count' => '',
        'will_attend_count' => ''
    );
}

Then in the while/for loops:

{
    $id = $result->getId();
    if (!isset($DataArray[$id])) { pre_map($DataArray[$id]); }
    $DataArray[$id]['no_response_yet_count'] = $NRCount;
}

The if (!isset($DataArray[$id])) is to make sure it doesn't wipe out the same index row, in case you happen to re-loop on the same ID. Thus, it will only map it once, then never again in the loop.

There are some other one-line shortcuts like maybe even using array_map(), but I was showing the long version, for full flexibility just in case.