CODEWITHSUNDEEP
javahashmap
Mp. Lo.
Mp. Lo.

Reputation: 35

Inserting into Hashmap of Hashmaps , Java

I have this function:

public void insert( String token, int docID) 
    {
        insertNormIdx( token,  docID); 
    }

which is being called continuously by the main program. docID is one document's ID and token is one word we found in the document.

So this function is being called many times, until all documents have been parsed. What I want to do, is to create one hashmap that has one entry docID and this should point to another hashmap that has the words (tokens) we found in the document with their count.

That is, if we found the word (token) 'the' 10 times in document (docID) '5' , I would like a structure that holds this information like: 5,the,10.

This is what i have done, but it doesnt really work, only keeps the first word from the documents:

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

    public void insertNormIdx(String token, int docID) 

   {
       HashMap<String, Integer> val = new HashMap<String, Integer>();

       if(!normal_idx.containsKey(docID)) 
        {

            val.put(token, 1);
            normal_idx.put(docID, val);
        }

       if (normal_idx.containsKey(docID))
            {

                if (normal_idx.get(docID).get(token)!=null) 
                {
                    val.put(token, normal_idx.get(docID).get(token)+1);

                    normal_idx.put(docID, val);
                }

            } 
   }

Upvotes: 2

Views: 789

Answers (3)

Darshan Mehta
Darshan Mehta

Reputation: 30839

You can use Java 8's computeIfAbsent method to put/merge values in map, e.g.:

public void insertNormIdx(String token, int docID) {
    normal_idx.computeIfAbsent(docID, k -> new HashMap<>()).merge(token, 1, (old, one) -> old + one);
}

Upvotes: 1

briarheart
briarheart

Reputation: 2006

Better way to do it:

public void insertNormIdx(String token, int docID) {
    Map<String, Integer> doc = normal_idx.get(docId);
    if (doc == null) {
        normal_idx.put(docId, doc = new HashMap<String, Integer>());
    }
    Integer counter = doc.get(token);
    if (counter == null)
        doc.put(token, 1);
    else
        doc.put(token, ++counter);
}

And by the way, do not use just bare HashMap, create class Document.

Upvotes: 1

shmosel
shmosel

Reputation: 50734

There's a lot of redundancy and mistakes in your code. The specific problem in your question is because there's no else to this if:

if (normal_idx.get(docID).get(token)!=null)

Therefore new tokens are never inserted.

But the whole code can be significantly improved. In Java 8, you can replace the entire method with:

normal_idx.computeIfAbsent(docID, k -> new HashMap<>())
        .merge(token, 1, Integer::sum);

If you're on an earlier Java version, you can try this:

HashMap<String, Integer> val = normal_idx.get(docID);
if (val == null) {
    val = new HashMap<String, Integer>();
    normal_idx.put(docID, val);
}

Integer count = val.get(token);
if (count == null) {
    val.put(token, 1);
} else {
    val.put(token, count + 1);
}

Upvotes: 2

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