Incrementing an array's value is causing warnings in the log - php

Question

I am trying to create an array that holds the count of each course we offer based on location and then instructor. Here is sample code
$courseCnt = array();
foreach($courseList as $course){
$courseCnt[$course['location']][$course['instructor']] += 1
}
This code creates the array properly and displays well but I get a bunch of warnings like:
Unidentified index "Orlando" for locations, Unidentified index "John
Smith" for instructor
I have found that if I just make it = 1 instead of += 1 the warnings go away but of course this makes every course for location/instructor 1 which is not good.
My next though was checking if it exists, if it doesn't, make it 1 and if it does += 1. Here is an example
if(isset($courseCnt[$course['location']][$course['instructor']]){
$courseCnt[$course['location']][$course['instructor']] += 1
}else{
$courseCnt[$course['location']][$course['instructor']] = 1
}
This results in the fatal error:
Cannot use string offset as an array
$course array structure is just a 2 dimensional array pulled from sql
Sample:
courseID location instructor
1 Orlando John Smith
2 Detroit Bill Murray

Answer 1

You are not checking if the location exists before checking for the instructor in your first line of the new version of the code. You need to check if it exists and create it in your $courseCnt array if it doesn't (as an empty array). After that, you can check for the instructor:
// Initialise the empty array
$courseCnt = array();
// Create location if not in array
if( ! isset($courseCnt[$course['location']])) {
$courseCnt[$course['location']] = array();
}
// Either increment the instructor or create with initial value of 1
if ( isset($courseCnt[$course['location']][$courseCnt[$course['instructor']]]) ) {
$courseCnt[$course['location']][$courseCnt[$course['instructor']]] += 1;
}
else
{
$courseCnt[$course['location']][$courseCnt[$course['instructor']]] = 1;
}
You've got a lot of square brackets going on in there, so you might find it easier to read if you use PHP's array_key_exists (documentation) instead of isset:
// Initialise the empty array
$courseCnt = array();
// Create location if not in array
if( ! array_key_exists($course['location'], $courseCnt)) {
$courseCnt[$course['location']] = array();
}
// Either increment the instructor or create with initial value of 1
if ( array_key_exists($course['instructor'], $courseCnt[$course['location']]) ) {
$courseCnt[$course['location']][$courseCnt[$course['instructor']]] += 1;
}
else
{
$courseCnt[$course['location']][$courseCnt[$course['instructor']]] = 1;
}