Finding the mean using RxJava

Question

I'm learning RxJava and this is what I attempted to find the mean of 'n' transactions.

List<Transaction> transactions = TransactionsStore.getTransactions();
BigDecimal nTransactions = new BigDecimal(transactions.size());
Observable.from(transactions)
 .map(transaction -> transaction.amount)
 .reduce(BigDecimal::add)
 .map(total -> total.divide(nTransactions, 2, BigDecimal.ROUND_DOWN))
 .map(mean -> String.format("The mean is %s", mean.toPlainString()))
 .subscribe(System.out::println);

I'd like to know if this could be done better.

Answer 1

Using RxJava-Math you can achieve the same result by this way:

List<Transaction> transactions = createRandomTransactions(10);
final Observable<Float> amountStream = Observable.from(transactions)
 .map(transaction -> transaction.amount);
MathObservable.averageFloat(amountStream)
 .map(mean -> String.format(Locale.US, "The mean is %.2f", mean))
 .subscribe(System.out::println);

Hope that helps!

• Quill: Please try to explain how this is an improvement of the existing code
• Ragunath Jawahar: Am I not losing precision here by using Float? My code sample uses BigDecimal, in case you didn't notice.
• Rodrigo Henriques: I'm just showing a different way to achieve the mean. I noticed that you are using BigDecimal, but you don't explicit defined this as a strong requirement in your question.