PHP array_multisort with some missing keys

Question

In two arrays I'm missing keys ($billing). Is there a way I can ignore, skip or just not take that given array iteration in to consideration and still sort the array?

I get the error message:

array_multisort(): Argument #1 is expected to be an array or a sort flag

foreach ($table as $key => $row)
{
   $billing[$key]  = $row['billing']['date_due'];
}

if ($_GET['billing']=='desc') {array_multisort($billing, SORT_DESC, $table);}
else {array_multisort($billing, SORT_ASC, $table);}

Answer 1

You can just check if a variable/key is set or is not empty:

<?php
foreach ($table as $key => $row) {
   $billing[$key]  = isset($row['billing']['date_due']) ? $row['billing']['date_due'] : null;
}

// $billing doesn't exist, if $table is empty
if (!empty($billing)) {
  array_multisort($billing, ($_GET['billing']=='desc' ? SORT_DESC : SORT_ASC), $table);
} else {
  array_multisort($table); // or simply sort($table);
}

Another way is to initialize $billing before foreach: $billing = [];.