Create a dictionary (array) from CSV data

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 looks like this (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. Without using classes.

Desired output of getDaysUnderTempDictionary(-10):

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

Instead of just storing hours as a single variable, store it in an array indexed by year. Once done with the CSV, loop over the array and divide each by 24, same as you did before.

This code has a mock CSV file for demo purposes, but is otherwise the same as yours:

function getDaysUnderTempDictionary(float $targetTemp): array {
    //This is just for mocking a CSV file
    $dataString = <<<EOT
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
EOT;
    $stream = fopen('php://memory', 'r+');
    fwrite($stream, $dataString);
    rewind($stream);
    
    $years = [];
    while ($data = fgetcsv($stream)) {
        $year = $data[0];
        if ($data[4] <= $targetTemp) {
            if(!isset($years[$year])){
                $years[$year] = 0;
            }
            $years[$year]++;
        }
    }
    foreach($years as $year => $hours){
        $years[$year] = $hours / 24;
    }
    return $years;
}

Demo: https://3v4l.org/RWFPK