From 99be993a400eea807afe8bc0441c5c95ac88cca2 Mon Sep 17 00:00:00 2001
From: Brent Worden <brentworden@apache.org>
Date: Tue, 24 May 2011 16:11:07 +0000
Subject: [PATCH] COLLECTIONS-306.  Added predicated subtract method to
 CollectionUtils.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1127123 13f79535-47bb-0310-9956-ffa450edef68
---
 .../commons/collections/CollectionUtils.java  | 24 ++++++++++++++++++-
 .../collections/TestCollectionUtils.java      | 18 ++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/src/java/org/apache/commons/collections/CollectionUtils.java b/src/java/org/apache/commons/collections/CollectionUtils.java
index b8d892418..a3490f2d0 100644
--- a/src/java/org/apache/commons/collections/CollectionUtils.java
+++ b/src/java/org/apache/commons/collections/CollectionUtils.java
@@ -33,6 +33,7 @@ import org.apache.commons.collections.collection.SynchronizedCollection;
 import org.apache.commons.collections.collection.TransformedCollection;
 import org.apache.commons.collections.collection.UnmodifiableBoundedCollection;
 import org.apache.commons.collections.collection.UnmodifiableCollection;
+import org.apache.commons.collections.functors.TruePredicate;
 
 /**
  * Provides utility methods and decorators for {@link Collection} instances.
@@ -235,10 +236,31 @@ public class CollectionUtils {
      * @see Collection#removeAll
      */
     public static <O> Collection<O> subtract(final Iterable<? extends O> a, final Iterable<? extends O> b) {
+        Predicate<O> p = TruePredicate.truePredicate();
+        return subtract(a, b, p);
+    }
+
+    /**
+     * Returns a new {@link Collection} containing <i>a</i> minus a subset of
+     * <i>b</i>.  Only the elements of <i>b</i> that satisfy the predicate
+     * condition, <i>p</i> are subtracted from <i>a</i>.
+     *
+     * @param a  the collection to subtract from, must not be null
+     * @param b  the collection to subtract, must not be null
+     * @param p  the condition used to determine which elements of <i>b</i> are
+     *        subtracted.
+     * @param <O> the generic type that is able to represent the types contained
+     *        in both input collections.
+     * @return a new collection with the results
+     * @see Collection#removeAll
+     */
+    public static <O> Collection<O> subtract(final Iterable<? extends O> a, final Iterable<? extends O> b, final Predicate<O> p) {
         ArrayList<O> list = new ArrayList<O>();
         addAll(list, a);
         for (O element : b) {
-            list.remove(element);
+            if (p.evaluate(element)) {
+                list.remove(element);
+            }
         }
         return list;
     }
diff --git a/src/test/org/apache/commons/collections/TestCollectionUtils.java b/src/test/org/apache/commons/collections/TestCollectionUtils.java
index e4a174ac3..a5b3bd42a 100644
--- a/src/test/org/apache/commons/collections/TestCollectionUtils.java
+++ b/src/test/org/apache/commons/collections/TestCollectionUtils.java
@@ -361,6 +361,24 @@ public class TestCollectionUtils extends MockTestCase {
         assertNull(freq2.get(1));
     }
 
+    @Test
+    public void testSubtractWithPredicate() {
+        // greater than 3
+        Predicate<Number> predicate = new Predicate<Number>() {
+            public boolean evaluate(Number n) {
+                return n.longValue() > 3L;
+            }
+        };
+        
+        Collection<Number> col = CollectionUtils.subtract(iterableA, collectionC, predicate);
+        Map<Number, Integer> freq2 = CollectionUtils.getCardinalityMap(col);
+        assertEquals(Integer.valueOf(1), freq2.get(1));
+        assertEquals(Integer.valueOf(2), freq2.get(2));
+        assertEquals(Integer.valueOf(3), freq2.get(3));
+        assertEquals(Integer.valueOf(2), freq2.get(4));
+        assertNull(freq2.get(5));
+    }
+
     @Test
     public void testIsSubCollectionOfSelf() {
         assertTrue(CollectionUtils.isSubCollection(collectionA, collectionA));