[CIShell-SVN] SF.net SVN: cishell:[1131] trunk/core/org.cishell.utilities/src/org/cishell /utilities/FrequencyMap.java

[<kon...@us...>]

Revision: 1131
          http://cishell.svn.sourceforge.net/cishell/?rev=1131&view=rev
Author:   kongchinhua
Date:     2010-09-07 19:15:01 +0000 (Tue, 07 Sep 2010)

Log Message:
-----------
Support Frequency counting
- It is important to use key with unmodified value with deep comp[are of equal function
- Safe to use with generic objects: String, Integer, etc
- Non-generic class need customized equal and hashcode method

Added Paths:
-----------
    trunk/core/org.cishell.utilities/src/org/cishell/utilities/FrequencyMap.java

Added: trunk/core/org.cishell.utilities/src/org/cishell/utilities/FrequencyMap.java
===================================================================
--- trunk/core/org.cishell.utilities/src/org/cishell/utilities/FrequencyMap.java	                        (rev 0)
+++ trunk/core/org.cishell.utilities/src/org/cishell/utilities/FrequencyMap.java	2010-09-07 19:15:01 UTC (rev 1131)
@@ -0,0 +1,107 @@
+package org.cishell.utilities;
+
+import java.util.HashMap;
+import java.util.Hashtable;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * FrequencyMap is a map of key with its emergence frequency.
+ * It supports two type of mapping structures: null key and 
+ * non-null key; by providing boolean value to enable 
+ * allowNullValue through constructor call. Add() method will
+ * add a new key if the key is not exist. Else it will increase
+ * the frequency by 1. sum() will return the count that 
+ * represents sum of all the frequency values in the map
+ * @author kongch
+ *
+ * @param <E>
+ */
+public class FrequencyMap <E> {
+	private Map<E, Frequency> itemToFrequencyMap;
+	private int count;
+	
+	public FrequencyMap(boolean allowNullValue) {
+		count = 0;
+		if (allowNullValue) {
+			itemToFrequencyMap = new HashMap<E, Frequency>();
+		} else {
+			itemToFrequencyMap = new Hashtable<E, Frequency>();
+		}
+	}
+	
+	/**
+	 * Add the given key to the map and increase the frequency by 1
+	 * @param key - key to be added
+	 */
+	public void add(E key) {
+		Frequency frequency;
+		
+		/* 
+		 * Get the Frequency object for the given key if key already exist. 
+		 * Else create a new Frequency object and add it to the map
+		 */
+		if (itemToFrequencyMap.containsKey(key)) {
+			frequency = itemToFrequencyMap.get(key);
+		} else {
+			frequency = new Frequency();
+			try {
+				itemToFrequencyMap.put(key, frequency);
+			} catch (NullPointerException  e) {
+				/* It is a non-null map. Throw a runtime exception */
+				String message = "FrequencyMap.add(E key) was called with a null key."
+						+ " If null support is desired, "
+						+ " construct FrequencyMap with allowNullValue = true";
+				throw new NullValueSupportException(message, e);
+			}
+		}
+		
+		/* increase frequency by 1 and also sum of all frequencies by 1 */
+		count++;
+		frequency.increase();
+	}
+	
+	/**
+	 * Retrieve a set of keys stored in this map 
+	 */
+	public Set<E> keySet() {
+		return itemToFrequencyMap.keySet();
+	}
+	
+	/**
+	 * Get the emergence frequency for the given key
+	 * @param key - item to be lookup
+	 * @return Return number of times the key exists
+	 * if lookup success. Return zero if key not exist
+	 */
+	public int getFrequency(E key) {
+		if (itemToFrequencyMap.containsKey(key)) {
+			return itemToFrequencyMap.get(key).getValue();
+		} else {
+			return 0;
+		}
+	}
+	
+	public int sum() {
+		return count;
+	}
+	
+	public boolean isEmpty() {
+		return itemToFrequencyMap.isEmpty();
+	}
+	
+	private class Frequency {
+		private int value;
+		public Frequency() {
+			value = 0;
+		}
+		
+		public void increase() {
+			value++;
+		}
+		
+		public int getValue() {
+			return value;
+		}
+	}
+}


Property changes on: trunk/core/org.cishell.utilities/src/org/cishell/utilities/FrequencyMap.java
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Added: svn:mime-type
   + text/plain


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