diff --git a/source/com/kemsky/Stream.as b/source/com/kemsky/Stream.as
index 45ad98c..9390221 100644
--- a/source/com/kemsky/Stream.as
+++ b/source/com/kemsky/Stream.as
@@ -1328,7 +1328,7 @@ package com.kemsky
 
         /**
          * Create new stream from original by removing duplicate items.
-         * @param callback is compare function <i>function(a:*, b:*):int</i>.
+         * @param callback is compare function <i>function(a:*, b:*):Boolean</i>.
          * @return new stream without duplicate values.
          * @example
          * <pre>
@@ -1340,23 +1340,30 @@ package com.kemsky
          */
         public function deduplicate(callback:Function = null):Stream
         {
-            var result:Stream;
-            if(callback == null)
+            var result:Stream = this.concat();
+            var i:int;
+            var j:int;
+
+            if(callback != null)
             {
-                var map:Dictionary = this.dictionary();
-                result = Stream.from(map);
+                for(i = 0; i < length - 1; i++)
+                {
+                    for(j = i + 1; j < length; j++)
+                    {
+                        if(callback(result.getItem(i), result.getItem(j)))
+                        {
+                            result.removeItem(j);
+                        }
+                    }
+                }
             }
             else
             {
-                //todo
-                result = this.concat();
-                var i:int;
-                var j:int;
                 for(i = 0; i < length - 1; i++)
                 {
                     for(j = i + 1; j < length; j++)
                     {
-                        if(callback(result.getItem(i), result.getItem(j)) == 0)
+                        if(result.getItem(i) === result.getItem(j))
                         {
                             result.removeItem(j);
                         }
diff --git a/source/com/kemsky/filters/mapped.as b/source/com/kemsky/filters/mapped.as
index d77697b..74fa09c 100644
--- a/source/com/kemsky/filters/mapped.as
+++ b/source/com/kemsky/filters/mapped.as
@@ -7,7 +7,8 @@ package com.kemsky.filters
         return function (item:*):Boolean
         {
             var v:* = toValue(item, val1);
-            return v is String ? map.hasOwnProperty(v): !(map[v] == null || map[v] === undefined);
+            var value:Object = map[v];
+            return !(value == null);
         };
     }
 }
diff --git a/testSrc/com/kemsky/TestStream.as b/testSrc/com/kemsky/TestStream.as
index 7d66750..833c706 100644
--- a/testSrc/com/kemsky/TestStream.as
+++ b/testSrc/com/kemsky/TestStream.as
@@ -26,10 +26,22 @@ package com.kemsky
         [Test]
         public function testDeduplicate():void
         {
-            var s:Stream = $(1, 2, 4, 3, 2, 1);
+            var s:Stream = $(1, 2, 2, 3, 1);
 
             var d1:Stream = s.deduplicate();
-            //assertEquals(d1.length, 4);
+            assertEquals(d1.length, 3);
+            assertEquals(d1.first, 1);
+            assertEquals(d1.second, 2);
+            assertEquals(d1.third, 3);
+
+            var s1:Stream = $("test", "you", "now");
+            var d2:Stream = s1.deduplicate(function(a:String, b:String):Boolean
+            {
+                return a.length == b.length;
+            });
+            assertEquals(d2.length, 2);
+            assertEquals(d2.first, "test");
+            assertEquals(d2.second, "you");
         }
 
         [Test]