com.clearspring.analytics.stream

Class StreamSummary<T>

java.lang.Object

com.clearspring.analytics.stream.StreamSummary<T>

Type Parameters:

T - type of data in the stream to be summarized

All Implemented Interfaces:

ITopK<T>, Externalizable, Serializable

public class StreamSummary<T>
extends Object
implements ITopK<T>, Externalizable

Based on the Space-Saving algorithm and the Stream-Summary data structure as described in: Efficient Computation of Frequent and Top-k Elements in Data Streams by Metwally, Agrawal, and Abbadi

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	StreamSummary.Bucket

Field Summary

Fields

Modifier and Type	Field and Description
protected DoublyLinkedList<StreamSummary.Bucket>	bucketList
protected int	capacity

Constructor Summary

Constructors

Constructor and Description
StreamSummary() For de-serialization
StreamSummary(byte[] bytes) For de-serialization
StreamSummary(int capacity)

Method Summary

Methods

Modifier and Type	Method and Description
void	fromBytes(byte[] bytes)
int	getCapacity()
protected void	incrementCounter(ListNode2<Counter<T>> counterNode, int incrementCount)
boolean	offer(T item) Algorithm: Space-Saving
boolean	offer(T item, int incrementCount) Algorithm: Space-Saving
Pair<Boolean,T>	offerReturnAll(T item, int incrementCount)
T	offerReturnDropped(T item, int incrementCount)
List<T>	peek(int k)
void	readExternal(ObjectInput in)
int	size()
byte[]	toBytes()
List<Counter<T>>	topK(int k)
String	toString()
void	writeExternal(ObjectOutput out)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

capacity

protected int capacity

bucketList

protected DoublyLinkedList<StreamSummary.Bucket> bucketList

Constructor Detail

StreamSummary

public StreamSummary(int capacity)

Parameters:

capacity - maximum size (larger capacities improve accuracy)

StreamSummary

public StreamSummary()

For de-serialization

StreamSummary

public StreamSummary(byte[] bytes)
              throws IOException,
                     ClassNotFoundException

For de-serialization

Parameters:

bytes -

Throws:

IOException

ClassNotFoundException

Method Detail

getCapacity

public int getCapacity()

offer

public boolean offer(T item)

Algorithm: Space-Saving

Specified by:

offer in interface ITopK<T>

Parameters:

item - stream element (e)

Returns:

false if item was already in the stream summary, true otherwise

offer

public boolean offer(T item,
            int incrementCount)

Algorithm: Space-Saving

Specified by:

offer in interface ITopK<T>

Parameters:

item - stream element (e)

incrementCount - - the increment count for the given count

Returns:

false if item was already in the stream summary, true otherwise

offerReturnDropped

public T offerReturnDropped(T item,
                   int incrementCount)

Parameters:

item - stream element (e)

Returns:

item dropped from summary if an item was dropped, null otherwise

offerReturnAll

public Pair<Boolean,T> offerReturnAll(T item,
                             int incrementCount)

Parameters:

item - stream element (e)

Returns:

Pair where isNewItem is the return value of offer() and itemDropped is null if no item was dropped

incrementCounter

protected void incrementCounter(ListNode2<Counter<T>> counterNode,
                    int incrementCount)

peek

public List<T> peek(int k)

Specified by:

peek in interface ITopK<T>

Returns:

top k elements offered (may be an approximation)

topK

public List<Counter<T>> topK(int k)

size

public int size()

Returns:

number of items stored

toString

public String toString()

Overrides:

toString in class Object

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

fromBytes

public void fromBytes(byte[] bytes)
               throws IOException,
                      ClassNotFoundException

Throws:

IOException

ClassNotFoundException

toBytes

public byte[] toBytes()
               throws IOException

Throws:

IOException