How to update specific field in CodeIgniter update?

Question

I'm using CodeIgniter framework for the easyappointments.org library. I'm trying to update the field data through the id of a row. Actually this is my code for the update:

return  $this->db
                ->update('ea_appointments', $appointment)
                ->where('ea_appointments.id', $appointment_id);

The problem's that the update method need two parameter (table to update, associative array with the fields name column of db). In my above function I pass only the $appointment_id, so the variable $appointment is empty and doesn't contain any associative array. I want to know how to update only the field data to 1. And remain the other field in the same value condition. This is the structure of the table:

id|book|start|end|notes|hash|unavailable|provider|data

Logic example:

previous condition row:

id => 0
book => example
start => 18/10/2015
end => 19/10/2015 
notes => empty
hash => akdjasldja
unavailable => false
provider => 5
data => 0 

I pass in the function $appointment_id with 0 value. I'm waiting this new result:

id => 0
book => example
start => 18/10/2015
end => 19/10/2015 
notes => empty
hash => akdjasldja
unavailable => false
provider => 5
data => 1

So the main problem is retrieve first the all field value of the specific row and later update? Or something like this. Could someone help me?

Solution

In my above function I pass only the $appointment_id, so the variable $appointment is empty and doesn't contain any associative array.

If you simply want to update the column data to 1 for appointment_id 0 then pass in an array with data for the key and 1 for the value.

$appointment_id = 0;
$appointment = array('data' => 1);    
$this->db->where('id', $appointment_id);
$this->db->update('ea_appointments', $appointment);