Where alias to filter

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

@@ -40,6 +40,7 @@
 import rx.operators.OperationDefer;
 import rx.operators.OperationDematerialize;
 import rx.operators.OperationFilter;
+import rx.operators.OperationWhere;
 import rx.operators.OperationMap;
 import rx.operators.OperationMaterialize;
 import rx.operators.OperationMerge;
@@ -722,6 +723,21 @@ public Boolean call(T t1) {
         });
     }
 
+    /**
+     * Filters an Observable by discarding any of its emissions that do not meet some test.
+     * <p>
+     * <img width="640" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/filter.png">
+     *
+     * @param that
+     *            the Observable to filter
+     * @param predicate
+     *            a function that evaluates the items emitted by the source Observable, returning <code>true</code> if they pass the filter
+     * @return an Observable that emits only those items in the original Observable that the filter evaluates as true
+     */
+    public static <T> Observable<T> where(Observable<T> that, Func1<T, Boolean> predicate) {
+        return _create(OperationWhere.where(that, predicate));
+    }
+
     /**
      * Converts an {@link Iterable} sequence to an Observable sequence.
      * 
@@ -2419,6 +2435,21 @@ public Boolean call(T t1) {
         });
     }
 
+    /**
+     * Filters an Observable by discarding any of its emissions that do not meet some test.
+     * <p>
+     * <img width="640" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/filter.png">
+     *
+     * @param predicate
+     *            a function that evaluates the items emitted by the source Observable, returning
+     *            <code>true</code> if they pass the filter
+     * @return an Observable that emits only those items in the original Observable that the filter
+     *         evaluates as <code>true</code>
+     */
+    public Observable<T> where(Func1<T, Boolean> predicate) {
+        return where(this, predicate);
+    }
+
     /**
      * Returns the last element of an observable sequence with a specified source.
      * 

rxjava-core/src/main/java/rx/operators/OperationWhere.java

@@ -0,0 +1,61 @@
+/**
+ * Copyright 2013 Netflix, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.operators;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import rx.Observable;
+import rx.Observer;
+import rx.Subscription;
+import rx.util.functions.Func1;
+
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+public final class OperationWhere {
+
+    public static <T> Func1<Observer<T>, Subscription> where(Observable<T> that, Func1<T, Boolean> predicate) {
+        return OperationFilter.filter(that, predicate);
+    }
+
+    public static class UnitTest {
+
+        @Test
+        public void testWhere() {
+            Observable<String> w = Observable.toObservable("one", "two", "three");
+            Observable<String> observable = Observable.create(where(w, new Func1<String, Boolean>() {
+
+                @Override
+                public Boolean call(String t1) {
+                    return t1.equals("two");
+                }
+            }));
+
+            @SuppressWarnings("unchecked")
+            Observer<String> aObserver = mock(Observer.class);
+            observable.subscribe(aObserver);
+            verify(aObserver, Mockito.never()).onNext("one");
+            verify(aObserver, times(1)).onNext("two");
+            verify(aObserver, Mockito.never()).onNext("three");
+            verify(aObserver, Mockito.never()).onError(any(Exception.class));
+            verify(aObserver, times(1)).onCompleted();
+        }
+    }
+
+}