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/*
* File: CollectionUtil.java
* Authors: Justin Basilico
* Company: Sandia National Laboratories
* Project: Cognitive Foundry
*
* Copyright March 25, 2008, Sandia Corporation.
* Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive
* license for use of this work by or on behalf of the U.S. Government. Export
* of this program may require a license from the United States Government.
* See CopyrightHistory.txt for complete details.
*
*/
package gov.sandia.cognition.collection;
import gov.sandia.cognition.annotation.CodeReview;
import gov.sandia.cognition.annotation.PublicationReference;
import gov.sandia.cognition.annotation.PublicationType;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
/**
* The {@code CollectionUtil} class implements static methods for dealing with
* {@code Collection} and {@code Iterable} objects. They are both put into the
* same utility class so that they can be interchanged without changing the
* method call.
*
* @author Justin Basilico
* @since 2.1
*/
@CodeReview(
reviewer="Kevin R. Dixon",
date="2008-12-02",
changesNeeded=false,
comments="Looks good."
)
public class CollectionUtil
{
/**
* Returns true if the given collection is null or empty.
*
* @param collection
* The collection to determine if it is null or empty.
* @return
* True if the given collection is null or empty.
*/
public static boolean isEmpty(
final Collection collection)
{
return collection == null || collection.isEmpty();
}
/**
* Returns true if the given iterable is null or empty.
*
* @param iterable
* The iterable to determine if it is null or empty.
* @return
* True if the given iterable is null or empty.
*/
public static boolean isEmpty(
final Iterable iterable)
{
if (iterable == null)
{
// It is null, so it is empty.
return true;
}
else if (iterable instanceof Collection)
{
return ((Collection) iterable).isEmpty();
}
else
{
return !iterable.iterator().hasNext();
}
}
/**
* Returns the Collection as an ArrayList. It first checks to see if
* data is already an ArrayList and returns the casted value. Otherwise,
* this method creates a new ArrayList from the data without copying each
* value.
* @param Type of data in the Collection.
* @param data Collection to return as an ArrayList.
* @return ArrayList of the given Collection.
*/
public static ArrayList asArrayList(
Iterable data )
{
if( data == null )
{
return null;
}
else if( data instanceof ArrayList )
{
return (ArrayList) data;
}
else if( data instanceof Collection )
{
return new ArrayList( (Collection) data );
}
else
{
final int num = CollectionUtil.size(data);
ArrayList retval = new ArrayList( num );
for( DataType value : data )
{
retval.add( value );
}
return retval;
}
}
/**
* Determines the size of the given collection, checking for null.
*
* @param collection
* The collection to get the size of.
* @return
* The size of the collection. If it is null, zero is returned.
*/
public static int size(
final Collection collection)
{
if (collection == null)
{
return 0;
}
else
{
return collection.size();
}
}
/**
* Determines the size of the given iterable. If it is null, zero is
* returned. If it is a {@code Collection}, then the size method is used.
* Otherwise, the iterable is iterated over to get the size.
*
* @param iterable
* The iterable to determine the size of.
* @return
* The size of the given iterable.
*/
public static int size(
final Iterable iterable)
{
if (iterable == null)
{
// The size is zero.
return 0;
}
else if (iterable instanceof Collection)
{
// Get the size from the collection. This cast is justified by
// not having to loop over all the elements.
return ((Collection) iterable).size();
}
else
{
// Cound up the elements in the iterable.
int counter = 0;
final Iterator iterator = iterable.iterator();
while (iterator.hasNext())
{
iterator.next();
counter++;
}
return counter;
}
}
/**
* Gets the first element from an iterable. If the iterable is null or
* empty, null is returned.
*
* @param
* The type of element.
* @param iterable
* The iterable to get the first element from.
* @return
* The first element from the iterable, if one exists. Otherwise,
* null.
*/
public static T getFirst(
final Iterable iterable)
{
if (iterable == null)
{
// No first element.
return null;
}
final Iterator iterator = iterable.iterator();
if (iterator.hasNext())
{
return iterator.next();
}
else
{
// No first element.
return null;
}
}
/**
* Returns the set of indices of the data array such that
* data[return[0..k-1]] <= data[return[k]] <= data[return[k+1...N-1]].
* This algorithm will partition the data set in O(N) time. This is
* faster than the typical sort and split time of O(N*log(N)).
* Note that the subsets data[return[0..k-1]] and data[return[k+1..N-1]]
* are themselves unsorted. Because of this, NRC calls "Selection is
* sorting's austere sister."
* @param Type of data to compare to.
* @param k
* kth largest value to split upon.
* @param data
* Data to partition, left unchanged by this method.
* @param comparator Comparator used to determine if two values
* are greater than, less than, or equal to each other.
* @return
* Indices into data so that
* data[return[0..k-1]] <= data[return[k]] <= data[return[k+1...N-1]].
*/
@PublicationReference(
author={
"William H Press",
"Saul A. Teukolsky",
"William T. Vetterling",
"Brian P. Flannery"
},
title="Numerical Recipes, Third Edition",
type=PublicationType.Book,
year=2007,
pages=1104,
notes="Loosely based on the selecti() function"
)
public static int[] findKthLargest(
int k,
ArrayList data,
Comparator comparator )
{
final int num = data.size();
final int[] indices = new int[ num ];
for( int i = 0; i < num; i++ )
{
indices[i] = i;
}
int leftIndex = 0;
int rightIndex = num-1;
while( true )
{
if( rightIndex <= leftIndex+1 )
{
if( rightIndex == leftIndex+1 )
{
swapIfAGreaterThanB(leftIndex, rightIndex, indices, data, comparator);
}
return indices;
}
else
{
final int mid = (leftIndex + rightIndex) / 2;
swapArrayValues(mid, leftIndex+1, indices);
swapIfAGreaterThanB(leftIndex, rightIndex, indices, data, comparator);
swapIfAGreaterThanB(leftIndex+1, rightIndex, indices, data, comparator);
swapIfAGreaterThanB(leftIndex, leftIndex+1, indices, data, comparator);
int i = leftIndex + 1;
final int originali = indices[i];
int j = rightIndex;
ComparableType valueOriginali = data.get(originali);
while( true )
{
// Find from the left a value that is >= valueOriginali
do
{
i++;
} while( comparator.compare( data.get(indices[i]), valueOriginali ) < 0 );
// Find from the right a value that is <= valueOriginali
do
{
j--;
} while( comparator.compare( data.get(indices[j]), valueOriginali ) > 0 );
if( j < i )
{
break;
}
swapArrayValues(i, j, indices);
}
indices[leftIndex+1] = indices[j];
indices[j] = originali;
if( j >= k )
{
rightIndex = j-1;
}
if( j <= k )
{
leftIndex = i;
}
}
}
}
/**
* Swaps the indices "a" and "b" in the array "indices" if the corresponding
* data values data[indices[a]] is greater than data[indices[b]].
* @param Type of data to compare to.
* @param a first index
* @param b second index
* @param indices array of indices to index into "data", which is
* modified by this method.
* @param data ArrayList of values, unchanged.
* @param comparator Comparator used to determine if two values
* are greater than, less than, or equal to each other.
* @return
* True if swapped, false if left alone.
*/
private static boolean swapIfAGreaterThanB(
int a,
int b,
int[] indices,
ArrayList data,
Comparator comparator )
{
final boolean doSwap = comparator.compare(
data.get(indices[a]), data.get(indices[b]) ) > 0;
if( doSwap )
{
swapArrayValues(a, b, indices);
}
return doSwap;
}
/**
* Swaps the two indexed values in the indices array.
* @param i1 First index
* @param i2 Second index
* @param indices Array of indices to swap
*/
private static void swapArrayValues(
int i1,
int i2,
int[] indices )
{
int temp = indices[i1];
indices[i1] = indices[i2];
indices[i2] = temp;
}
/**
* Creates a partition of the given data into "numPartition" roughly equal
* sets, preserving their pre-existing sequential ordering, with the
* nonzero remainder elements going into the final partition.
*
* @param Type of data to partition.
* @param data Collection of data to partition
* @param numPartitions Number of partitions to create.
* @return
* List of Lists of size data.size()/numPartitions, with the remainder of
* data elements going into the final partition.
*/
public static ArrayList> createSequentialPartitions(
Iterable data,
int numPartitions )
{
final int numData = CollectionUtil.size( data );
final int numEach = numData / numPartitions;
ArrayList> retval =
new ArrayList>( numPartitions );
if( data instanceof List )
{
@SuppressWarnings("unchecked")
List list = (List) data;
int beginIndex = 0;
int endIndex = beginIndex + numEach;
for( int i = 0; i < numPartitions; i++ )
{
if( i == numPartitions-1 )
{
endIndex = numData;
}
retval.add( list.subList(beginIndex, endIndex) );
beginIndex = endIndex;
endIndex += numEach;
}
}
else
{
int index = 0;
Iterator iterator = data.iterator();
for( int n = 0; n < numPartitions; n++ )
{
// The remainder goes into the final partition
int numThis = (n < (numPartitions-1)) ? numEach : (numData-index);
ArrayList partition = new ArrayList( numThis );
for( int i = 0; i < numThis; i++ )
{
partition.add( iterator.next() );
index++;
}
retval.add( partition );
}
}
return retval;
}
/**
* Returns the indexed value into the {@code Iterable}. It first checks to
* see if the {@code Iterable} is a {@code List}, and if so calls the get
* method. Otherwise, it walks the {@code Iterable} to get to the element.
*
* @param
* The type of data.
* @param iterable
* The iterable to pull the value from.
* @param index
* The 0-based index to pull from the iterable.
* @return
* The value at the given spot in the iterable.
* @throws IndexOutOfBoundsException
* If the index is less than zero or greater than or equal to the
* number of elements in the iterable.
*/
public static DataType getElement(
final Iterable iterable,
int index)
{
if (iterable instanceof List)
{
return ((List) iterable).get(index);
}
else
{
if (index < 0)
{
// Bad index.
throw new IndexOutOfBoundsException("index must be >= 0");
}
for (DataType v : iterable)
{
if (index == 0)
{
return v;
}
index--;
}
// Bad index.
throw new IndexOutOfBoundsException("index >= iterable size");
}
}
/**
* Removes and returns the indexed value into the {@code Iterable}. It
* first checks to see if the {@code Iterable} is a {@code List}, and if so
* calls the remove method. Otherwise, it walks the {@code Iterable} to
* get to the element and remove it. This only works on {@code Iterable}s
* that are {@code List}s or whose {@code Iterator} implements the optional
* {@code remove} method.
*
* @param
* The type of data.
* @param iterable
* The iterable to remove the value from.
* @param index
* The 0-based index to remove from the iterable.
* @return
* The value removed from the given index in the iterable.
* @throws IndexOutOfBoundsException
* If the index is less than zero or greater than or equal to the
* number of elements in the iterable.
* @throws UnsupportedOperationException
* If the iterable does not support remove.
*/
public static DataType removeElement(
final Iterable iterable,
int index)
{
if (iterable instanceof List)
{
return ((List) iterable).remove(index);
}
else
{
if (index < 0)
{
// Bad index.
throw new IndexOutOfBoundsException("index must be >= 0");
}
Iterator iterator = iterable.iterator();
while (iterator.hasNext())
{
DataType value = iterator.next();
if (index == 0)
{
iterator.remove();
return value;
}
index--;
}
// Bad index.
throw new IndexOutOfBoundsException("index >= iterable size");
}
}
/**
* Performs a toString on each element given iterable with a given delimiter
* between elements.
*
* @param list
* The list to call toString on each element for.
* @param delimiter
* The delimiter.
* @return
* A string with the toString on each element in the list called with
* a given delimiter between elements. If null is given, then
* "null" is returned. If an empty list is given, "" is returned.
*/
public static String toStringDelimited(
final Iterable list,
final String delimiter)
{
if (list == null)
{
return "null";
}
final StringBuffer result = new StringBuffer();
final Iterator iterator = list.iterator();
if (iterator.hasNext())
{
result.append(iterator.next());
}
while (iterator.hasNext())
{
result.append(delimiter);
result.append(iterator.next());
}
return result.toString();
}
}
