Double division behaving wrongly

Question

I have a HashMap called List<String, Intger> wordFreqMap whose size is 234

wordFreqMap = {radiology=1, shift=2, mummy=1, empirical=1, awful=1, geoff=1, .......}

I want to calculate the term frequency of each word.

term frequency = frequency of term / total number of terms

public static Map<String, Double> getTFMap (Map<String, Integer> wordFreqMap)
    {
        Map<String, Double> tfMap = new HashMap<String, Double>();
        int noOfTerms = wordFreqMap.size();
        Double tf;

        for (Entry<String, Integer> word : wordFreqMap.entrySet() ) 
        {
                tf = (double) ( word.getValue() / noOfTerms );
                tfMap.put(word.getKey(), tf );
        }
        return tfMap;
    }

My problem is that, tfMap is returning {radiology=0.0, shift=0.0, mummy=0.0, empirical=0.0, awful=0.0, geoff=0.0, .....}

I don't understand why it returns 0.0 for every term. How do I fix it?

I should get something like {radiology=0.00427, shift=0.00854, ...}

The cast to `double` in your code is closing the barn door after the horse has bolted :) — Sergey Kalinichenko, Sep 09 '14 at 15:42
possible duplicate of [Division of integers in Java](http://stackoverflow.com/questions/7220681/division-of-integers-in-java) — Dennis Meng, Sep 09 '14 at 15:45

score 9 · Accepted Answer · answered Sep 09 '14 at 15:41

You're performing an integer division and then type casting:

tf = (double) ( word.getValue() / noOfTerms );
                ^-----integer division----^

Type cast one of the elements in the division to convert into a floating point division:

tf = ((double)word.getValue()) / noOfTerms;

score 2 · Answer 2 · answered Sep 09 '14 at 15:41

2

You are doing integer division and then casting that answer to a double. What you need to do is cast one of the two values to a double first, and then do division on it. That should get you the answer you desire.

answered Sep 09 '14 at 15:41

AGreenman

225
1
7

score 1 · Answer 3 · answered Sep 09 '14 at 15:43

1

Integer/Integer is an Integer which is casted to a Double so ,it remains an Integer expanded to a Double.

Change it to

 tf =  ( (double)word.getValue() / noOfTerms );

answered Sep 09 '14 at 15:43

Kumar Abhinav

6,565
2
24
35

Thusitha Thilina Dayaratne · Answer 4 · 2014-09-09T15:58:15.860

what you are doing is dividing an integer by another integer and then trying to cast that to a double. int/int is a int do though you cast that to a double you will not get the actual value with decimal points.

int/int -> int

What you should do is either cast word.getValue() or noOfterms to double then

int/double -> double
double/int -> double
double/double -> double

e.g.

  tf =  (double)word.getValue()/noOfTerms;

or

tf =  word.getValue()/(double)noOfTerms;

Double division behaving wrongly

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