Get all the keys of an array and in case the key has no value, return the value

I’ve just come across a problem, which apparently looks simple, but I can’t find a solution. I have the following array in PHP:

[
  "name" => "user"
  0 => "created_at"
  "email" => "mail"
]

And I need to get an array like this:

[
  "name"
  "created_at"
  "email"
]

As you can see, I only need to obtain the original keys from the array, but in case a value from the original array does not have an associated value, then return the value instead of the key.

I have tried several ways using the following methods:

array_flip()
array_keys()
array_values()

I would appreciate in advance anyone who could help me.

>Solution :

Loop through the array and add the desired values to your new array:

$a = [
  "name" => "user",
  0 => "created_at",
  "email" => "mail",
];

$b = [];
foreach ( $a as $k => $v ) {
    $b[] = ( $k ? $k : $v );
}

print_r($b);
/*
Array
(
    [0] => name
    [1] => created_at
    [2] => email
)
*/

For a more sophisticated determination of which key(s) to keep, replace the first $k in the ternary expression with a function that tests $k for validity:

$b[] = ( test($k) ? $k : $v );
// ...
function test($k) {
  return ! is_number($k); // For example
}