Easiest Way to Sort a List of Words by Occurance

Question

What is the best/easiest way to sort a large list of words (10,000-20,000) by the number of times they occur in the list, in Java. I tried a basic implementation but I get an ou

Answer 1

Have you considered using String interning in addition to a hashmap? String interning means all same Strings use the same memory location in order to save memory. Based on an answer Sort a Map by values (Java) please see below:

import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.TreeMap;
public class WordOccurSortExample {

public static void main(String[] args) {
        new  WordOccurSortExample();        
}

public WordOccurSortExample()
{
    ArrayList occuringWords = new ArrayList();
    occuringWords.add("Menios".intern());
    occuringWords.add("Menios".intern());
    occuringWords.add("Menios".intern());
    occuringWords.add("Menios".intern());
    occuringWords.add("Moo".intern());
    occuringWords.add("Moo".intern());
    occuringWords.add("Moo".intern());
    occuringWords.add("Moo".intern());
    occuringWords.add("Moo".intern());
    occuringWords.add("Boo".intern());
    occuringWords.add("Boo".intern());
    occuringWords.add("Boo".intern());

    HashMap occurances = new HashMap();

    Iterator it = occuringWords.iterator();
    String word;
    Integer count;
    while(it.hasNext())
    {
        word = it.next();

        if((count = occurances.get(word))==null)
        occurances.put(word, 1);
        else
        occurances.put(word, new Integer(count+1)); 
    }       

    ValueComparator bvc =  new ValueComparator(occurances);
    TreeMap sorted_map = new TreeMap(bvc);

    System.out.println("unsorted map: "+occuringWords);
    sorted_map.putAll(occurances);
    System.out.println("results: "+sorted_map);
}


class ValueComparator implements Comparator {

    HashMap base;
    public ValueComparator(HashMap base) {
        this.base = base;
    }

    // Note: this comparator imposes orderings that are inconsistent with equals.    
    public int compare(String a, String b) {
        if (base.get(a) >= base.get(b)) {
            return -1;
        } else {
            return 1;
        } // returning 0 would merge keys
    }

}

}