added where operation to Observable

Author: prabirshrestha

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.
      *