Dictionary from CSV (PHP)

I need to write a function that takes temperature as an input and returns a dictionary with years as keys and number of days as values.

CSV file (year, month, day, hour, temperature):

2019,1,1,0,0.1
2019,1,1,1,0.4
2019,1,1,2,0.8
2019,1,1,3,1.3
2019,1,1,4,1.8
...
2020,1,1,0,-3.9

The number of days is calculated by another function which I already have. It takes a year and a temperature and returns how many days in a given year the temperature was equal to or below the given temperature. Since the data is about hours, not days, the number of hours is found and then divided by 24.

The function:

function getDaysUnderTemp(int $targetYear, float $targetTemp): float {

    $file = fopen("data/temperatures-filtered.csv", "r");
    $hours = 0;

    while ($data = fgetcsv($file)) {
        if ($data[0] == $targetYear and $data[4] <= $targetTemp) {
            $hours ++;
        }
    }

    fclose($file);
    return $hours / 24;
}

So as an example getDaysUnderTemp(2019, -10) returns 13.92.

This is a function I am asking about as I'm not sure how it might be done:

function getDaysUnderTempDictionary(float $targetTemp): array {
    $file = fopen("data/temperatures-filtered.csv", "r");

    while ($data = fgetcsv($file)) {
        ???
    }
    
    fclose($file);
    return [];
}

The problem is I don't understand how an already written function could be implemented in this new one, and then create a required dictionary from all this data.

Desired output:

getDaysUnderTempDictionary(-10);

Array
(
    [2019] => 3.88
    [2020] => 0.21
    [2021] => 13.92
)

If I were doing this, I would read all the data into an array in raw form
then produce whatever other structures I needed.

I am going to write this as a class:

class TempCalculator {
    private $data;
    private $arr;

    const YEAR = 0;
    const TEMP = 4;

    public function __construct($filename) {
        $this->data = array_map('str_getcsv', file($filename));
    }

    public function getHoursBelowTemperature($temperature) : array {
        $this->arr = array();

        foreach ($this->data as $row) {
            $year = $row[self::YEAR];
            $temperatureValue = floatval($row[self::TEMP]);
            if ($temperatureValue < $temperature) {
                if (!array_key_exists($year, $this->arr)) {
                    $this->arr[$year] = 0;
                }
                $this->arr[$year]++;
            }
        }
        // Walk the array and divide all the hours by 24
        array_walk($this->arr, function (&$value) {
            $value /= 24;
        });
        return $this->arr;
    }

    public getDaysUnderTemp($year, $temp) : float {
        $hours = 0;
        foreach ($this->data as $row) {
            if ($row[self::YEAR] == $targetYear && $row[self::TEMP] <= $targetTemp) {
                $hours ++;
            }
        }
        return $hours / 24;
    }    
}

You can call it like this:

$tempCalculator = new TempCalculator('temperatures.csv');
$result = $tempCalculator->getHoursBelowTemperature(0);
print_r($result);

$result2 = $tempCalculator->getDaysUnderTemp(1.5);
print_r($result2);