Original data   Passed to frontend  Changes by user      Data being sent back
  id=827
val1=arthur     val1=arthur                              val1=arthur
val2=ford       val2=ford                                val2=ford
val3=tricia     val3=tricia         val3=trillian        val3=trillian
val4=zaphod     val4=zaphod                              val4=zaphod
val5=marvin     val5=marvin                              val5=marvin
   .
   .
   .

2014-04-08: User 'douglas' changed val3 in row #827

2014-04-08: User 'eoin' changed val1, val2 and val3 in row #137

$updated_data = ['first_name' => 'John', 'last_name' => 'White'];
$original_data = ['first_name' => 'Peter', 'last_name' => 'White'];

$updated_fields = array_keys(array_diff_assoc($updated_data, $original_data));

print_r($updated_fields);  # List of updated fields