rainfall_best.java

public static double bestPracticeMean(String town, String strng) {
       return parseTemp(town, strng).stream()
           .collect(averagingDouble(n -> n));
}

public static double bestPracticeVariance(String town, String strng) {
       double mean = mean(town, strng);
       if (mean == -1.0) return -1.0;
       
       return parseTemp(town, strng).stream()
           .collect(averagingDouble(n -> (n - mean) * (n - mean)));
}
      
private static List<Double> parseTemp(String town, String strng) {
       List<Double> temps = new ArrayList<>();
       for (String line : strng.split("\\n")) {
         String[] data = line.split(":");
         if (town.equals(data[0])) {
           for (String weather : data[1].split(",")) {
             String[] temp = weather.split("\\s");
             temps.add(Double.parseDouble(temp[1]));
           }
           break;
         }
       }
        if (temps.isEmpty()) temps.add(-1.0);
       
       return temps;
}