Can someone help me debug this error: Undefined offset: 0? - php

Question

I am creating a function that calculate the quantity of sold tickets, and here is my code:
public function get_quantity($tickets_info){
$i = 0; //$i is the starting point of the loop
$k = 0;
$Qty = 1; // this is used to save the quantity of tickets, by default there is always one ticket
$index = array();
$quantity = array();
for($j = 1; $j < count($tickets_info); $j++) {
// if the ticket_id are the same, then increase the quantity by one
if($tickets_info[$i]['ticket_id'] == $tickets_info[$j]['ticket_id'])
{
$Qty++;
}
// if the ticket_id are not the same, then push the quantity into an array and remember the index
else
{
$idx = $j;//remember the index of the next first different ticket_id
$i = $j;//find the next starting point
$index[$k] = $idx;//push back the index of the next different ticket_id
$quantity[$k] = $Qty;//save quantity into the array
$k++;//increase the index poniter
$Qty = 1;//reset quantity back to one
}
}
// push the last quantity into the array
$quantity[$k+1] = $Qty;
//assign the ticket information into a new array
for($m = 0; $m < count($quantity); $m++){
$ticket[$m] = $tickets_info[$m];
}
//create the finally array, combine ticket information with quantity
$n = 0;
foreach($ticket as $row)
{
$row['Qty'] = $quantity[$n++];
}
return $ticket;
}
$ticket_info is a 2-D array which is generated from a SQL, and it has a structure like this:
$ticket_info
(
[0]=>array
(
[ticket_id] => 0001
[purchase_time] => 2014/01/02
....
)
[1]=>array
(
[ticket_id] => 0001
[purchase_time] => 2014/01/02
....
)
[2]=>array
(
[ticket_id] => 0001
[purchase_time] => 2014/01/02
....
)
....
)
Basically, if the tickets have the same ticket_id that means they have been bought at the same time (but in the database, I recorded them separately for a specific purpose), so I need to add them up and get the quantity.
I'm not familiar with PHP arrays, so I write my algorithm in C++ and tested it. It works fine. However, when I tried to write the real code in PHP, I got 2 errors:
For line, $ticket[$m] = $tickets_info[$m]; Message: Undefined offset: 0
For line, $row['Qty'] = $quantity[$n++]; Message: Undefined offset: 0
I don't know why there is no index 0, maybe I didn't initialize the array correctly or I didn't pass the data in $ticket_info in the right format? Can someone help me look at this code?

Answer 1

Do a check before you try access that index:
if (!empty($ticket) && !empty($tickets_info)) {
$ticket[$m] = $tickets_info[$m];
}