$stations = [];
$fp = fopen('measurements.txt', 'r');
while ($data = fgetcsv($fp, null, ';')) {    if (!isset($stations[$data[0]])) {        $stations[$data[0]] = [            $data[1],            $data[1],            $data[1],            1        ];    } else {        $stations[$data[0]][3] ++;        $stations[$data[0]][2] += $data[1];        if ($data[1] < $stations[$data[0]][0]) {            $stations[$data[0]][0] = $data[1];        }        if ($data[1] > $stations[$data[0]][1]) {            $stations[$data[0]][1] = $data[1];        }    }}
ksort($stations);
echo '{';foreach($stations as $k=>&$station) {    $station[2] = $station[2]/$station[3];    echo $k, '=', $station[0], '/', $station[2], '/', $station[1], ', ';}echo '}';

// ...while ($data = fgets($fp, 999)) {    $pos = strpos($data, ';');    $city = substr($data, 0, $pos);    $temp = substr($data, $pos+1, -1);// ...

18 | $stations[$city][3] ++;   | // ...23 | if ($temp > $stations[$city][1]) {

$station = &$stations[$city];$station[3] ++;$station[2] += $temp;// instead of$stations[$city][3] ++;$stations[$city][2] += $data[1];

if ($temp < $station[0]) {    $station[0] = $temp;}if ($temp > $station[1]) {    $station[1] = $temp;}

$temp = (float)substr($data, $pos+1, -1);

18 | $station = &$stations[$city];   | // ...23 | } elseif ($temp > $station[1]) {

while ($data = fgets($fp)) {
// instead ofwhile ($data = fgets($fp, 999)) {

$file = 'measurements.txt';
$threads_cnt = 16;
/** * Get the chunks that each thread needs to process with start and end position. * These positions are aligned to \n chars because we use `fgets()` to read * which itself reads till a \n character. * * @return array */function get_file_chunks(string $file, int $cpu_count): array {    $size = filesize($file);
    if ($cpu_count == 1) {        $chunk_size = $size;    } else {        $chunk_size = (int) ($size / $cpu_count);    }
    $fp = fopen($file, 'rb');
    $chunks = [];    $chunk_start = 0;    while ($chunk_start < $size) {        $chunk_end = min($size, $chunk_start + $chunk_size);
        if ($chunk_end < $size) {            fseek($fp, $chunk_end);            fgets($fp); // moves fp to next \n char            $chunk_end = ftell($fp);        }
        $chunks[] = [            $chunk_start,            $chunk_end        ];
        $chunk_start = $chunk_end+1;    }
    fclose($fp);    return $chunks;}
/** * This function will open the file passed in `$file` and read and process the * data from `$chunk_start` to `$chunk_end`. * * The returned array has the name of the city as the key and an array as the * value, containing the min temp in key 0, the max temp in key 1, the sum of * all temperatures in key 2 and count of temperatures in key 3. * * @return array */ $process_chunk = function (string $file, int $chunk_start, int $chunk_end): array {    $stations = [];    $fp = fopen($file, 'rb');    fseek($fp, $chunk_start);    while ($data = fgets($fp)) {        $chunk_start += strlen($data);        if ($chunk_start > $chunk_end) {            break;        }        $pos2 = strpos($data, ';');        $city = substr($data, 0, $pos2);        $temp = (float)substr($data, $pos2+1, -1);        if (isset($stations[$city])) {            $station = &$stations[$city];            $station[3] ++;            $station[2] += $temp;            if ($temp < $station[0]) {                $station[0] = $temp;            } elseif ($temp > $station[1]) {                $station[1] = $temp;            }        } else {            $stations[$city] = [                $temp,                $temp,                $temp,                1            ];        }    }    return $stations;};
$chunks = get_file_chunks($file, $threads_cnt);
$futures = [];
for ($i = 0; $i < $threads_cnt; $i++) {    $runtime = new \parallel\Runtime();    $futures[$i] = $runtime->run(        $process_chunk,        [            $file,            $chunks[$i][0],            $chunks[$i][1]        ]    );}
$results = [];
for ($i = 0; $i < $threads_cnt; $i++) {    // `value()` blocks until a result is available, so the main thread waits    // for the thread to finish    $chunk_result = $futures[$i]->value();    foreach ($chunk_result as $city => $measurement) {        if (isset($results[$city])) {            $result = &$results[$city];            $result[2] += $measurement[2];            $result[3] += $measurement[3];            if ($measurement[0] < $result[0]) {                $result[0] = $measurement[0];            }            if ($measurement[1] < $result[1]) {                $result[1] = $measurement[1];            }        } else {            $results[$city] = $measurement;        }    }}
ksort($results);
echo '{', PHP_EOL;foreach($results as $k=>&$station) {    echo "\t", $k, '=', $station[0], '/', ($station[2]/$station[3]), '/', $station[1], ',', PHP_EOL;}echo '}', PHP_EOL;