CODEWITHSUNDEEP
javaprecision
Olivier_s_j
Olivier_s_j

Reputation: 5182

Math with bigdecimal resulting in 0

I'm trying to figure a problem out with BigDecimal. My code:

BigDecimal tweetcount = new BigDecimal(3344048);
BigDecimal emotionCountBig = new BigDecimal(855937);
BigDecimal emotionCountSentenceBig = new BigDecimal(84988); 

MathContext mc = new MathContext(64);
PMI[cnt] = (emotionCountSentenceBig.divide((tweetcount.multiply(emotionCountBig,mc)),RoundingMode.HALF_UP));

What I'd like to do is: emotionCountSentenceBig/(emotionCountBig*tweetcount)

(The values can be bigger)

If i try this I get a zero, which is not possible. Any help ?

Upvotes: 0

Views: 107

Answers (2)

assylias
assylias

Reputation: 328588

You need to specify the MathContext for the division too:

emotionCountSentenceBig.divide(tweetcount.multiply(emotionCountBig, mc), mc);

That gives the expected result:

2.969226352632111794036880818610913852084810652372969382467557947E-8

Now as rightly commented by @PeterLawrey you could use doubles instead:

public static void main(String[] args) throws Exception {
    double tweetcount = 3344048;
    double emotionCount = 855937;
    double emotionCountSentence = 84988;

    double result = emotionCountSentence / (tweetcount * emotionCount);

    System.out.println("result = " + result);
}

which prints:

result = 2.9692263526321117E-8

Note that if you use:

double result = 84988 / (3344048 * 855937);

you are actually doing your operations (* and /) on integer and it will return 0. You can prevent it by explicitly using a double, for example (note the d):

double result = 84988d / (3344048d * 855937);

Upvotes: 4

Peter Lawrey
Peter Lawrey

Reputation: 533472

I would use double

int tweetcount = 3344048;
int emotionCountBig = 855937;
int emotionCountSentenceBig = 84988;

double pmi = emotionCountSentenceBig/((double) tweetcount * emotionCountBig);
System.out.println(pmi);

prints

2.9692263526321117E-8

which is close to the answer using BigDecimal

2.969226352632111794036880818610913852084810652372969382467557947E-8

Upvotes: 2

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