使用HashMap [Java]计算文档频率

Question

I am trying to calculate document frequency (ie in how many documents each word appears), example:

Doc1: this phone is the greatest phone ever.
Doc2: what's your phone number.

Result:

this              1
phone             2
is                1
the               1
ever              1
what's            1
your              1
number            1

I have the following code in Java

HashMap<String, String> wordDoc = new HashMap<String, String>();
HashMap<String, Integer> countDfIndex = new HashMap<String, Integer>();

if (!wordDoc.containsKey(word)) {
    wordDoc.put(word,docno);
    countDfIndex.put(word, 1);
}
if (wordDoc.get(word)!=null) {
    if(!wordDoc.containsValue(docno)) {
        wordDoc.put(word,docno);
        countDfIndex.put(word, countDfIndex.get(word)+1);
    }
}

I am not getting the right result, Kindly help!!

Answer 1

I assume you're trying to count number of documents containing the respective word, rather than total number of occurrences.

If so:

Map<String, Integer> countDfIndex = new HashMap<String, Integer>();

for (... document : documents) {
    Set<String> alreadyAdded = new HashSet<String>(); // new empty set for each document

    ...

    if (!alreadyAdded.contains(word)) {
        if (!countDfIndex.containsKey(word) {
            countDfIndex.put(word, 1);
        } else {
            countDfIndex.put(word, countDfIndex.get(word) + 1);
        }
        alreadyAdded.add(word); // don't add the word anymore if found again in the document
    }

}

Answer 2

public static void add(Map<String, Integer> map, String word) {
    map.put(word, map.containsKey(word) ? map.get(word) + 1 : 1);
}

---

for (String i : s.replace(".", "").split(" ")) add(map, i);

where,

• map = new HashMap<String, Integer>();
• s = "this phone is the greatest phone ever. what's your phone number."

Finally, the map contains

{the=1, ever=1, number=1, phone=3, this=1, what's=1, is=1, your=1, greatest=1}

Answer 3

HashMap<String, Integer> countDfIndex = new HashMap<String, Integer>();

if (!countDfIndex.containsKey(word))
    {
      countDfIndex.put(word, 1);
    }
else{
int i =countDfIndex.get(word);
countDfIndex.put(word,i+1);
}
for(Map.Entry<String,Integer> pair: countDfIndex.entrySet()){   

                int count=pair.getValue();
                String word=pair.getKey();
                System.out.println("word is "+word+"count is "+count);

            }