Cakephp 3: view.ctp sum two variables - sum

Question

I have a view that shows an associated array of Revenues. I have made a collection in the controller to isolate two variables that I need to add together and display as currency.
public function view($id = null)
{
$annualOperatingBudget = $this->AnnualOperatingBudgets->get($id, [
'contain' => ['Azinstitutions', 'BudgetExpenses', 'BudgetExpenses.ExpenseTitles', 'BudgetRevenues', 'BudgetRevenues.RevenueTitles']
]);
$collection = new Collection($annualOperatingBudget->budget_revenues);
$revenuesGroup1 = $collection->match(['revenue_title.revenue_group' => 1 ]);
$revenuesGroup2 = $collection->match(['revenue_title.revenue_group' => 2 ]);
$tuitionAndFees = $collection->match(['revenue_title.revenue_title' => 'Tuition and Fees']);
$lessScholarshipAllowance = $collection->match(['revenue_title.revenue_title' => '- less Scholarship Allowance']);
$this->set(compact('annualOperatingBudget', $annualOperatingBudget,'revenuesGroup1', 'revenuesGroup2', 'tuitionAndFees', 'lessScholarshipAllowance'));
}
I am able to see the variables with the debug kit:
annualOperatingBudget (array)
revenuesGroup1 (array)
revenuesGroup2 (array)
tuitionAndFees (array)
4 (App\Model\Entity\BudgetRevenue)
id 5
annual_operating_budget_id 1
revenue 1278
revenue_title_id 5
revenue_title (array)
lessScholarshipAllowance (array)
5 (App\Model\Entity\BudgetRevenue)
id 6
annual_operating_budget_id 1
revenue -257
revenue_title_id 6
revenue_title (array)
I would like to add the two 'revenue' s together
I tried:
<?= $this->Number->currency(
($tuitionAndFees->revenue) + ($lessScholarShipAllowance->revenue),
'USD', ['places' => 1])
?>
But I get several errors:
Notice (8): Undefined property: Cake\Collection\Iterator\FilterIterator::$revenue [ROOT\plugins\Twit\src\Template\AnnualOperatingBudgets\view.ctp, line 49]
Notice (8): Undefined variable: lessScholarShipAllowance [ROOT\plugins\Twit\src\Template\AnnualOperatingBudgets\view.ctp, line 49]
Notice (8): Trying to get property of non-object [ROOT\plugins\Twit\src\Template\AnnualOperatingBudgets\view.ctp, line 49]

Answer 1

You have to iterate the $tuitionAndFees and the $lessScholarShipAllowance before trying to get the revenue property. Something like this:
foreach($tuitionAndFees as $tuitionAndFee){
echo $tuitionAndFee->revenue
}

Answer 2

If all you need in the view is the total of all tuition and fees, you can use
$tuitionAndFees = $collection
->match(['revenue_title.revenue_title' => 'Tuition and Fees'])
->sumOf('revenue');
This will return just the sum of the matched items. Do something similar for $lessScholarShipAllowance, and then in your view, simply
$this->Number->currency($tuitionAndFees + $lessScholarShipAllowance,
'USD', ['places' => 1])