Combine CSV rows, but merge differences

csv-merge.php

<?php /* This changes the CSV into another CSV. But merges duplicated fields. */
$handle = fopen("CLUBEXP.csv", "r");
$row = 0;
$ClubNumberList = array();

while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
    // ID
    $ClubNumber = $data[0];
	
	// Day
    $day = $data[19];
    // Times
    $start = $data[20];
    $end = $data[21];
    
    // Type of Group
    $type = $data[18].' - ';
    
    $ClubTDays = $type . $day.': '.$start.' - '.$end;

    if ( array_key_exists($ClubNumber, $ClubNumberList) ) {
        $ClubNumberList[$ClubNumber][] = $ClubTDays;
    } else {
        $ClubNumberList[$ClubNumber] = array($ClubTDays);
    }
    $row++;
}

if (count($row) > 0) {
    $handle = fopen('CLUBEXP_merged.CSV', 'w');
    if (!$handle) throw new Exception("Can't open CSV file for merged data");
    foreach($ClubNumberList as $ClubNumber => $vals) {
        array_unshift($vals, $ClubNumber);
        if (!fputcsv($handle, $vals)) throw new Exception("Can't write data to merged CSV file");
    }
    fclose($handle);
}

echo '<pre>';
print_r( $ClubNumberList );
echo '</pre>';

Can you share the CSV which you have taken as a reference?

This was 9 years ago, absolutely no idea.