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[COLLECTIONS-296] Added CollectionUtils#merge methods to merge two sorted Collections. Thanks to Julius Davies for the report and patch.

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git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1469577 13f79535-47bb-0310-9956-ffa450edef68
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Thomas Neidhart 2013-04-18 21:06:40 +00:00
parent fd5c46d080
commit 5ea7e3a7d4
3 changed files with 243 additions and 0 deletions
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4
src/changes/changes.xml
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@ -22,6 +22,10 @@
<body> <body>
<release version="4.0" date="TBA" description="Next release"> <release version="4.0" date="TBA" description="Next release">
<action issue="COLLECTIONS-296" dev="tn" type="add" due-to="Julius Davies">
Added methods "CollectionUtils#merge(...)" to merge two sorted Collections
into a sorted List using the standard O(n) merge algorithm.
</action>
<action issue="COLLECTIONS-429,COLLECTION-434" dev="tn" type="add" due-to="Adrian Nistor, Mert Guldur"> <action issue="COLLECTIONS-429,COLLECTION-434" dev="tn" type="add" due-to="Adrian Nistor, Mert Guldur">
Added method "CollectionUtils#containsAll(Collection, Collection)" with guaranteed Added method "CollectionUtils#containsAll(Collection, Collection)" with guaranteed
runtime complexity of O(n + m) and space complexity of O(n). This method may yield much runtime complexity of O(n + m) and space complexity of O(n). This method may yield much

147
src/main/java/org/apache/commons/collections4/CollectionUtils.java
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@ -19,6 +19,7 @@ package org.apache.commons.collections4;
import java.lang.reflect.Array; import java.lang.reflect.Array;
import java.util.ArrayList; import java.util.ArrayList;
import java.util.Collection; import java.util.Collection;
import java.util.Comparator;
import java.util.Enumeration; import java.util.Enumeration;
import java.util.HashMap; import java.util.HashMap;
import java.util.HashSet; import java.util.HashSet;
@ -1438,6 +1439,152 @@ public class CollectionUtils {
} }
} }
//-----------------------------------------------------------------------
/**
* Merges two sorted Collections, a and b, into a single, sorted List
* such that the natural ordering of the elements is retained.
* <p>
* Uses the standard O(n) merge algorithm for combining two sorted lists.
*
* @param <O> the element type
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @return a new sorted List, containing the elements of Collection a and b
* @throws IllegalArgumentException if either collection is null
*/
public static <O extends Comparable<? super O>> List<O> merge(Collection<? extends O> a,
Collection<? extends O> b) {
return merge(a, b, ComparatorUtils.<O>naturalComparator(), true);
}
/**
/**
* Merges two sorted Collections, a and b, into a single, sorted List
* such that the natural ordering of the elements is retained.
* <p>
* Uses the standard O(n) merge algorithm for combining two sorted lists.
*
* @param <O> the element type
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @param includeDuplicates if {@code true} duplicate elements will be retained, otherwise
* they will be removed in the output collection
* @return a new sorted List, containing the elements of Collection a and b
* @throws IllegalArgumentException if either collection is null
*/
public static <O extends Comparable<? super O>> List<O> merge(final Collection<? extends O> a,
final Collection<? extends O> b,
final boolean includeDuplicates) {
return merge(a, b, ComparatorUtils.<O>naturalComparator(), includeDuplicates);
}
/**
* Merges two sorted Collections, a and b, into a single, sorted List
* such that the ordering of the elements according to Comparator c is retained.
* <p>
* Uses the standard O(n) merge algorithm for combining two sorted lists.
*
* @param <O> the element type
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @param c the comparator to use for the merge.
* @return a new sorted List, containing the elements of Collection a and b
* @throws IllegalArgumentException if either collection or the comparator is null
*/
public static <O> List<O> merge(final Collection<? extends O> a, final Collection<? extends O> b,
final Comparator<? super O> c) {
return merge(a, b, c, true);
}
/**
* Merges two sorted Collections, a and b, into a single, sorted List
* such that the ordering of the elements according to Comparator c is retained.
* <p>
* Uses the standard O(n) merge algorithm for combining two sorted lists.
*
* @param <O> the element type
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @param c the comparator to use for the merge.
* @param includeDuplicates if {@code true} duplicate elements will be retained, otherwise
* they will be removed in the output collection
* @return a new sorted List, containing the elements of Collection a and b
* @throws IllegalArgumentException if either collection or the comparator is null
*/
public static <O> List<O> merge(final Collection<? extends O> a, final Collection<? extends O> b,
final Comparator<? super O> c, final boolean includeDuplicates) {
if (a == null || b == null) {
throw new IllegalArgumentException("The collections must not be null");
}
if (c == null) {
throw new IllegalArgumentException("The comparator must not be null");
}
final List<O> mergedList = new ArrayList<O>(a.size() + b.size());
// if either collection is empty, just return the other one
if (a.isEmpty() || b.isEmpty()) {
mergedList.addAll(a.isEmpty() ? b : a);
return mergedList;
}
final Iterator<? extends O> it1 = a.iterator();
final Iterator<? extends O> it2 = b.iterator();
O o1 = it1.next();
O o2 = it2.next();
O last = null;
while (true) {
final int x = c.compare(o1, o2);
if (x <= 0) {
last = addItemToList(o1, mergedList, last, includeDuplicates);
if (it1.hasNext()) {
o1 = it1.next();
} else {
// a is empty, so add current element of b
last = addItemToList(o2, mergedList, last, includeDuplicates);
break;
}
} else {
last = addItemToList(o2, mergedList, last, includeDuplicates);
if (it2.hasNext()) {
o2 = it2.next();
} else {
// b is empty, so add current element of a
last = addItemToList(o1, mergedList, last, includeDuplicates);
break;
}
}
}
// add the remaining elements from the non-empty iterator
final Iterator<? extends O> it = it1.hasNext() ? it1 : it2;
while (it.hasNext()) {
last = addItemToList(it.next(), mergedList, last, includeDuplicates);
}
return mergedList;
}
/**
* Adds an item to the specified list.
*
* @param item the item to add
* @param list the list to use
* @param lastItem the last added item, may be null
* @param includeDuplicates whether duplicate entries are allowed
* @return the last added item
*/
private static <E> E addItemToList(final E item, final List<E> list, final E lastItem,
final boolean includeDuplicates) {
if (includeDuplicates || lastItem == null || !lastItem.equals(item)) {
list.add(item);
return item;
} else {
return lastItem;
}
}
//----------------------------------------------------------------------- //-----------------------------------------------------------------------
/** /**
* Returns a collection containing all the elements in <code>collection</code> * Returns a collection containing all the elements in <code>collection</code>

92
src/test/java/org/apache/commons/collections4/CollectionUtilsTest.java
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@ -70,6 +70,16 @@ public class CollectionUtilsTest extends MockTestCase {
*/ */
private Collection<Integer> collectionC = null; private Collection<Integer> collectionC = null;
/**
* Sorted Collection of {@link Integer}s
*/
private Collection<Integer> collectionD = null;
/**
* Sorted Collection of {@link Integer}s
*/
private Collection<Integer> collectionE = null;
/** /**
* Collection of {@link Integer}s, bound as {@link Number}s * Collection of {@link Integer}s, bound as {@link Number}s
*/ */
@ -96,6 +106,8 @@ public class CollectionUtilsTest extends MockTestCase {
private Iterable<Number> iterableB2 = null; private Iterable<Number> iterableB2 = null;
private Collection<Integer> emptyCollection = new ArrayList<Integer>(1);
@Before @Before
public void setUp() { public void setUp() {
collectionA = new ArrayList<Integer>(); collectionA = new ArrayList<Integer>();
@ -134,6 +146,25 @@ public class CollectionUtilsTest extends MockTestCase {
collectionC2 = new LinkedList<Number>(collectionC); collectionC2 = new LinkedList<Number>(collectionC);
iterableA2 = collectionA2; iterableA2 = collectionA2;
iterableB2 = collectionB2; iterableB2 = collectionB2;
collectionD = new ArrayList<Integer>();
collectionD.add(1);
collectionD.add(3);
collectionD.add(3);
collectionD.add(3);
collectionD.add(5);
collectionD.add(7);
collectionD.add(7);
collectionD.add(10);
collectionE = new ArrayList<Integer>();
collectionE.add(2);
collectionE.add(4);
collectionE.add(4);
collectionE.add(5);
collectionE.add(6);
collectionE.add(6);
collectionE.add(9);
} }
@Test @Test
@ -1553,4 +1584,65 @@ public class CollectionUtilsTest extends MockTestCase {
expect(iterator.hasNext()).andReturn(true); expect(iterator.hasNext()).andReturn(true);
expect(iterator.next()).andReturn(t); expect(iterator.next()).andReturn(t);
} }
@Test(expected=IllegalArgumentException.class)
public void mergeException1() {
CollectionUtils.merge(collectionA, null);
}
@Test(expected=IllegalArgumentException.class)
public void mergeException2() {
CollectionUtils.merge(collectionA, collectionC, null);
}
@Test
public void testMerge() {
List<Integer> result = CollectionUtils.merge(emptyCollection, emptyCollection);
assertEquals("Merge empty with empty", 0, result.size());
result = CollectionUtils.merge(collectionA, emptyCollection);
assertEquals("Merge empty with non-empty", collectionA, result);
List<Integer> result1 = CollectionUtils.merge(collectionD, collectionE);
List<Integer> result2 = CollectionUtils.merge(collectionE, collectionD);
assertEquals("Merge two lists 1", result1, result2);
List<Integer> combinedList = new ArrayList<Integer>();
combinedList.addAll(collectionD);
combinedList.addAll(collectionE);
Collections.sort(combinedList);
assertEquals("Merge two lists 2", combinedList, result2);
final Comparator<Integer> reverseComparator =
ComparatorUtils.reversedComparator(ComparatorUtils.<Integer>naturalComparator());
result = CollectionUtils.merge(emptyCollection, emptyCollection, reverseComparator);
assertEquals("Comparator Merge empty with empty", 0, result.size());
Collections.reverse((List<Integer>) collectionD);
Collections.reverse((List<Integer>) collectionE);
Collections.reverse(combinedList);
result1 = CollectionUtils.merge(collectionD, collectionE, reverseComparator);
result2 = CollectionUtils.merge(collectionE, collectionD, reverseComparator);
assertEquals("Comparator Merge two lists 1", result1, result2);
assertEquals("Comparator Merge two lists 2", combinedList, result2);
}
@Test
public void testMergeIgnoreDuplicates() {
List<Integer> result1 = CollectionUtils.merge(collectionD, collectionE, false);
List<Integer> result2 = CollectionUtils.merge(collectionE, collectionD, false);
assertEquals("Merge two lists 1 - ignore duplicates", result1, result2);
Set<Integer> combinedSet = new HashSet<Integer>();
combinedSet.addAll(collectionD);
combinedSet.addAll(collectionE);
List<Integer> combinedList = new ArrayList<Integer>(combinedSet);
Collections.sort(combinedList);
assertEquals("Merge two lists 2 - ignore duplicates", combinedList, result2);
}
} }