Storing data for a linked list in a pair in Java

Question

I am trying to create a linked list that will take a large amount of data, either integers or strings, and get the frequency that they occur. I know how to create a basic linked list that would achieve this but since the amount of data is so large, I want to find a quicker way to sort through the data, instead of going through the entire linked list every time I call a certain method. In order to do this I need to make a Pair of <Object, Integer> where the Object is the data and the integer is the frequency it occurs.

So far I have tried creating arrays and lists that would help me sort out the data but cannot figure out how to get it into a Pair that represents the data and frequency. If you have any ideas that can help me at least get started that would be much appreciated.

Answer 1

First of all you must define your own data type, let's say

public FrequencyCount<T> implements Comparable<FrequencyCount<T>>
{
  public final T data;
  public int frequency;

  public int compareTo(FrequencyCount<T> other) {
    // implement this method to choose your correct natural ordering
  }
}

With a similar object everything becomes trivial:

List<FrequencyCount<Some>> data = new ArrayList<FrequencyCount<Some>>();
Collections.sort(data);

Set<FrequencyCount<Some>> sortedData = new TreeSet<FrequencyCount<Some>>(data);

Answer 2

You could place all values into a List, create a Set from it and then iterate over the Set to find the frequency in the List using Collections.frequency: http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#frequency(java.util.Collection,%20java.lang.Object)

List<Integer> allValues = ...;
Set<Integer> uniqueValues = new HashSet<Integer>(allValues);
for(Integer val : uniqueValues) {
    int frequency = Collections.frequency(allValues, val);
// use val and frequency as key and value as you wish
}