library/src/main/java/com/datatorrent/lib/math/Change.java

/*
 * Copyright (c) 2013 DataTorrent, Inc. ALL Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.datatorrent.lib.math;

import com.datatorrent.api.DefaultInputPort;
import com.datatorrent.api.DefaultOutputPort;
import com.datatorrent.api.annotation.OutputPortFieldAnnotation;
import com.datatorrent.lib.util.BaseNumberValueOperator;

/**
 * Operator compares data values arriving on input port with base value input operator.
 * 
 * <p>
 * Arriving base value is stored in operator for comparison, old base value is overwritten.&nbsp;
 * This emits &lt;change in value,percentage change&gt;.
 * Operator expects values arriving on data input port and base value input operator.
 * Change in value and percentage change in values are emitted on separate ports.<br>
 * This operator can not be partitioned, since copies won't get consecutive operators. <br>
 * This is StateFull operator, tuples that arrive on base port are kept in
 * cache forever.<br>
 * <br>
 * <b>Input Ports</b>:<br>
 * <b>data</b>: expects V extends Number, Data values<br>
 * <b>base</b>: expects V extends Number, Base Value stored for comparison<br>
 *
 * <b>Output Ports</b>:<br>
 * <b>change</b>: emits V extends Number,  Diff from base value<br>
 * <b>percent</b>: emits Doubl, percent change in value compared to base value.<br>
 * <br>
 * <br>
 * <b>Properties</b>:<br>
 * <b>inverse</b>: if set to true the key in the filter will block tuple<br>
 * <b>filterBy</b>: List of keys to filter on<br>
 * <br>
 * <b>Specific compile time checks</b>: None<br>
 * <b>Specific run time checks</b>: None<br>
 * <br>
 *
 * <br>
 * @displayName Change
 * @category Math
 * @tags change, key value, numeric, percentage
 * @since 0.3.3
 */
public class Change<V extends Number> extends BaseNumberValueOperator<V>
{
        /**
	 * Input data port that takes a number.
	 */
	public final transient DefaultInputPort<V> data = new DefaultInputPort<V>()
	{
		/**
		 * Process each key, compute change or percent, and emit it.
		 */
		@Override
		public void process(V tuple)
		{
			if (baseValue != 0) { // Avoid divide by zero, Emit an error tuple?
				double cval = tuple.doubleValue() - baseValue;
				change.emit(getValue(cval));
				percent.emit((cval / baseValue) * 100);
			}
		}
	};
        
        /**
	 * Input port that takes a number&nbsp; It stores the value for base comparison. 
	 */
	public final transient DefaultInputPort<V> base = new DefaultInputPort<V>()
	{
		/**
		 * Process each key to store the value. If same key appears again update
		 * with latest value.
		 */
		@Override
		public void process(V tuple)
		{
			if (tuple.doubleValue() != 0.0) { // Avoid divide by zero, Emit an error
																				// tuple?
				baseValue = tuple.doubleValue();
			}
		}
	};
	
	/**
	 * Output port that emits change in value compared to base value.
	 */
	@OutputPortFieldAnnotation(optional = true)
	public final transient DefaultOutputPort<V> change = new DefaultOutputPort<V>();
	
	/**
	 * Output port that emits percent change in data value compared to base value.
	 */
	@OutputPortFieldAnnotation(optional = true)
	public final transient DefaultOutputPort<Double> percent = new DefaultOutputPort<Double>();
	
	/**
	 * baseValue is a state full field. It is retained across windows.
	 */
	private double baseValue = 0;
}