How to convert Long to BigDecimal while also using a Stream

Question

I'm struggling to understand how can I make the following code work.

The field count_human_dna of my stat class is of type BigDecimal, with setting the type as Long this works, but I need to change it to BigDecimal, can somehow tell me how could I make this work for BigDecimal field?

stat.setCount_human_dna(dnaSamples.stream()
    .filter(x -> x.getType().equals("Human"))
    .collect(Collectors.counting()));

This code is counting all the dnaSamples which type belong to Human.

Answer 1

The most simple and efficient way to do is to use terminal operation count() which returns the number of elements in the stream as long and then convert into BigDecimal:

stat.setCount_human_dna(getDNACount(dnaSamples));

public static BigDecimal getDNACount(Collection<Sample> dnaSamples) {
    long humanSamples = dnaSamples.stream()
        .filter(x -> x.getType().equals("Human"))
        .count();

    return BigDecimal.valueOf(humanSamples);
}

---

And you can produce the result of type BigDecimal directly from the stream using reduce() a terminal operation:

stat.setCount_human_dna(getDNACount(dnaSamples));

public static BigDecimal getDNACount(Collection<Sample> dnaSamples) {
    return dnaSamples.stream()
        .filter(x -> x.getType().equals("Human"))
        .reduce(BigDecimal.ZERO,
                (total, next) -> total.add(BigDecimal.ONE),
                BigDecimal::add);
}

Sidenote: I'm not an expert in such questions as DNA analysis, but the result of this reduction will always be a whole number. You might consider utilizing BigInteger instead of BigDecimal.