Merge pull request #159 from mairbek/lastOrDefault

Implemented LastOrDefault Operator

Author: benjchristensen

language-adaptors/rxjava-groovy/src/test/groovy/rx/lang/groovy/ObservableTests.groovy

@@ -233,6 +233,18 @@ def class ObservableTests {
         }
     }
 
+    @Test
+    public void testLastOrDefault() {
+        def val = Observable.toObservable("one", "two").lastOrDefault("default", { x -> x.length() == 3})
+        assertEquals("two", val)
+    }
+
+    @Test
+    public void testLastOrDefault2() {
+        def val = Observable.toObservable("one", "two").lastOrDefault("default", { x -> x.length() > 3})
+        assertEquals("default", val)
+    }
+
     def class AsyncObservable implements Func1<Observer<Integer>, Subscription> {
 
         public Subscription call(final Observer<Integer> observer) {

rxjava-core/src/main/java/rx/Observable.java

@@ -685,6 +685,61 @@ public static <T> Observable<T> last(final Observable<T> that) {
         return _create(OperationLast.last(that));
     }
 
+    /**
+     * Returns the last element of an observable sequence, or a default value if no value is found.
+     * @param source the source observable.
+     * @param defaultValue a default value that would be returned if observable is empty.
+     * @param <T> the type of source.
+     * @return the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     */
+    public static <T> T lastOrDefault(Observable<T> source, T defaultValue) {
+        boolean found = false;
+        T result = null;
+
+        for (T value : source.toIterable()) {
+            found = true;
+            result = value;
+        }
+
+        if (!found) {
+            return defaultValue;
+        }
+
+        return result;
+    }
+
+    /**
+     * Returns the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     * @param source the source observable.
+     * @param defaultValue a default value that would be returned if observable is empty.
+     * @param predicate a predicate function to evaluate for elements in the sequence.
+     * @param <T> the type of source.
+     * @return the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     */
+    public static <T> T lastOrDefault(Observable<T> source, T defaultValue, Func1<T, Boolean> predicate) {
+        return lastOrDefault(source.filter(predicate), defaultValue);
+    }
+
+    /**
+     * Returns the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     * @param source the source observable.
+     * @param defaultValue a default value that would be returned if observable is empty.
+     * @param predicate a predicate function to evaluate for elements in the sequence.
+     * @param <T> the type of source.
+     * @return the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     */
+    public static <T> T lastOrDefault(Observable<T> source, T defaultValue, Object predicate){
+        @SuppressWarnings("rawtypes")
+        final FuncN _f = Functions.from(predicate);
+
+        return lastOrDefault(source, defaultValue, new Func1<T, Boolean>() {
+            @Override
+            public Boolean call(T args) {
+                return (Boolean) _f.call(args);
+            }
+        });
+    }
+
     /**
      * Applies a function of your choosing to every notification emitted by an Observable, and returns
      * this transformation as a new Observable sequence.
@@ -2030,6 +2085,38 @@ public Observable<T> last() {
         return last(this);
     }
 
+    /**
+     * Returns the last element, or a default value if no value is found.
+     *
+     * @param defaultValue a default value that would be returned if observable is empty.
+     * @return the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     */
+    public T lastOrDefault(T defaultValue) {
+        return lastOrDefault(this, defaultValue);
+    }
+
+    /**
+     * Returns the last element that matches the predicate, or a default value if no value is found.
+     *
+     * @param defaultValue a default value that would be returned if observable is empty.
+     * @param predicate    a predicate function to evaluate for elements in the sequence.
+     * @return the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     */
+    public T lastOrDefault(T defaultValue, Func1<T, Boolean> predicate) {
+        return lastOrDefault(this, defaultValue, predicate);
+    }
+
+    /**
+     * Returns the last element that matches the predicate, or a default value if no value is found.
+     *
+     * @param defaultValue a default value that would be returned if observable is empty.
+     * @param predicate    a predicate function to evaluate for elements in the sequence.
+     * @return the last element of an observable sequence that matches the predicate, or a default value if no value is found.
+     */
+    public T lastOrDefault(T defaultValue, Object predicate) {
+        return lastOrDefault(this, defaultValue, predicate);
+    }
+
     /**
      * Applies a function of your choosing to every item emitted by an Observable, and returns this
      * transformation as a new Observable sequence.
@@ -2743,6 +2830,55 @@ public Subscription call(Observer<String> observer) {
 
         }
 
+        @Test
+        public void testLastOrDefault1() {
+            Observable<String> observable = toObservable("one", "two", "three");
+            assertEquals("three", observable.lastOrDefault("default"));
+        }
+
+        @Test
+        public void testLastOrDefault2() {
+            Observable<String> observable = toObservable();
+            assertEquals("default", observable.lastOrDefault("default"));
+        }
+
+        @Test
+        public void testLastOrDefault() {
+            Observable<Integer> observable = toObservable(1, 0, -1);
+            int last = observable.lastOrDefault(-100, new Func1<Integer, Boolean>() {
+                @Override
+                public Boolean call(Integer args) {
+                    return args >= 0;
+                }
+            });
+            assertEquals(0, last);
+        }
+
+        @Test
+        public void testLastOrDefaultWrongPredicate() {
+            Observable<Integer> observable = toObservable(-1, -2, -3);
+            int last = observable.lastOrDefault(0, new Func1<Integer, Boolean>() {
+                @Override
+                public Boolean call(Integer args) {
+                    return args >= 0;
+                }
+            });
+            assertEquals(0, last);
+        }
+
+        @Test
+        public void testLastOrDefaultWithPredicate() {
+            Observable<Integer> observable = toObservable(1, 0, -1);
+            int last = observable.lastOrDefault(0, new Func1<Integer, Boolean>() {
+                @Override
+                public Boolean call(Integer args) {
+                    return args < 0;
+                }
+            });
+
+            assertEquals(-1, last);
+        }
+
         private static class TestException extends RuntimeException {
 
         }