diff --git a/src/components/RoomList.js b/src/components/RoomList.js
index 45dadf0..971ecc4 100644
--- a/src/components/RoomList.js
+++ b/src/components/RoomList.js
@@ -13,11 +13,11 @@ class RoomList extends React.Component {
     }
 
     render() {
-        const { selected, rooms, roomActions } = this.props;
+        const { selected, roomMap, roomActions } = this.props;
 
         const children = [];
 
-        for (const [room_name, room_data] of rooms) {
+        for (const [room_name, room_data] of roomMap) {
             const onClick = (event) => {
                 roomActions.select(room_name);
             };
@@ -43,7 +43,7 @@ class RoomList extends React.Component {
 }
 
 RoomList.propTypes = {
-    rooms: PropTypes.object.isRequired,
+    roomMap: PropTypes.object.isRequired,
     roomActions: PropTypes.shape({
         getList: PropTypes.func.isRequired
     }).isRequired,
diff --git a/src/containers/RoomsPane.js b/src/containers/RoomsPane.js
index 5debe7d..09ce6d6 100644
--- a/src/containers/RoomsPane.js
+++ b/src/containers/RoomsPane.js
@@ -15,7 +15,7 @@ class RoomsPane extends React.Component {
     }
 
     render() {
-        const { loginUserName, params, rooms, roomActions } = this.props;
+        const { loginUserName, params, roomMap, roomActions } = this.props;
 
         let roomName;
         let roomChat;
@@ -23,7 +23,7 @@ class RoomsPane extends React.Component {
         if (params && params.roomName) {
             roomName = decodeURIComponent(atob(params.roomName));
 
-            const { membership, messages, showUsers } = rooms.get(roomName);
+            const { membership, messages, showUsers } = roomMap.get(roomName);
             const room = {
                 name: roomName,
                 membership,
@@ -42,7 +42,7 @@ class RoomsPane extends React.Component {
         return (
             <div id="rooms-pane">
                 <RoomList
-                    rooms={rooms}
+                    roomMap={roomMap}
                     roomActions={roomActions}
                     selected={roomName}
                 />
@@ -59,12 +59,12 @@ RoomsPane.propTypes = {
     params:        PropTypes.shape({
         roomName: PropTypes.string
     }),
-    rooms:         ImmutablePropTypes.orderedMap.isRequired,
-    roomActions:   PropTypes.object.isRequired
+    roomMap:     ImmutablePropTypes.orderedMap.isRequired,
+    roomActions: PropTypes.object.isRequired
 };
 
 const mapStateToProps = (state) => ({
-    rooms: state.rooms.rooms,
+    roomMap: state.rooms.roomMap,
     loginUserName: state.login.username
 });
 
diff --git a/src/reducers/rooms.js b/src/reducers/rooms.js
index 26ee3e7..5dbc7ad 100644
--- a/src/reducers/rooms.js
+++ b/src/reducers/rooms.js
@@ -10,10 +10,13 @@ import {
 } from "../constants/ActionTypes";
 
 const initialState = {
-    rooms: Immutable.OrderedMap()
+    roomMap:        Immutable.OrderedMap(),
+    roomNameByHash: Immutable.Map()
 };
 
-const reduceRoomList = (oldRoomMap, roomList) => {
+const reduceRoomList = (state, roomList) => {
+    const { roomMap, roomNameByHash } = state;
+
     // First sort the room list by room name
     roomList.sort(([ roomName1 ], [ roomName2 ]) => {
         if (roomName1 < roomName2) {
@@ -31,123 +34,124 @@ const reduceRoomList = (oldRoomMap, roomList) => {
         // Transform room_data.messages to an immutable list.
         newRoomData.messages = Immutable.List(newRoomData.messages);
         // Get the old room data.
-        const oldRoomData = oldRoomMap.get(roomName);
+        const roomData = roomMap.get(roomName);
         // Merge the old data and the new data, overwriting with new data if
         // conflicting.
         const mergedRoomData = {
-            ...oldRoomData,
+            ...roomData,
             ...newRoomData
         };
         newRoomMap = newRoomMap.set(roomName, mergedRoomData);
     }
-    return newRoomMap;
+    return {
+        ...state,
+        roomMap: newRoomMap,
+        roomNameByHash
+    };
 };
 
-const reduceReceiveMessage = (rooms, { variant, data }) => {
+const reduceReceiveMessageRoom = (roomData, { variant, data }) => {
     switch (variant) {
         case "RoomJoinResponse":
-        {
-            const { room_name } = data;
-            const room = rooms.get(room_name);
-            return rooms.set(room_name, {
-                ...room,
+            return {
+                ...roomData,
                 membership: "Member"
-            });
-        }
+            };
 
         case "RoomLeaveResponse":
-        {
-            const room_name = data;
-            const room = rooms.get(room_name);
-            return rooms.set(room_name, {
-                ...room,
+            return {
+                ...roomData,
                 membership: "NonMember"
-            });
-        }
-
-        case "RoomListResponse":
-            return reduceRoomList(rooms, data.rooms);
+            };
 
         case "RoomMessageResponse":
         {
-            const { room_name, user_name, message } = data;
-            const room_data = rooms.get(room_name);
-            if (!room_data) {
-                console.log(`Error: room "${room_name} not found`);
-                return rooms;
-            }
-            const new_room_data = {
-                ...room_data,
-                messages: room_data.messages.push({ user_name, message })
+            const { user_name, message } = data;
+            return {
+                ...roomData,
+                messages: roomData.messages.push({ user_name, message })
             };
-            return rooms.set(room_name, new_room_data);
         }
-
-        default:
-            return rooms;
     }
 };
 
-export default (state = initialState, action) => {
-    const { type, payload } = action;
-    switch (type) {
-        case SOCKET_RECEIVE_MESSAGE:
+const reduceReceiveMessage = (state, message) => {
+    const { variant, data } = message;
+    switch (variant) {
+        case "RoomJoinResponse":
+        case "RoomLeaveResponse":
+        case "RoomMessageResponse":
+        {
+            const { room_name } = data;
+            const roomData = state.roomMap.get(room_name);
+            const roomMap = state.roomMap.set(room_name,
+                reduceReceiveMessageRoom(roomData, { variant, data })
+            );
             return {
                 ...state,
-                rooms: reduceReceiveMessage(state.rooms, payload)
+                roomMap
             };
+        }
 
-        case ROOM_MESSAGE:
+        case "RoomListResponse":
+            return reduceRoomList(state, data.rooms);
+
+        default:
             return state;
+    }
+};
 
+const reduceRoom = (roomData, { type, payload }) => {
+    switch (type) {
         case ROOM_JOIN:
-        {
-            const rooms = state.rooms.set(payload, {
-                ...state.rooms.get(payload),
-                membership: "Joining"
-            });
             return {
-                ...state,
-                rooms
+                ...roomData,
+                membership: "Joining"
             };
-        }
 
         case ROOM_LEAVE:
-        {
-            const rooms = state.rooms.set(payload, {
-                ...state.rooms.get(payload),
-                membership: "Leaving"
-            });
             return {
-                ...state,
-                rooms
+                ...roomData,
+                membership: "Leaving"
             };
-        }
 
         case ROOM_SHOW_USERS:
-        {
-            const rooms = state.rooms.set(payload, {
-                ...state.rooms.get(payload),
+            return {
+                ...roomData,
                 showUsers: true
-            });
+            };
+
+        case ROOM_HIDE_USERS:
             return {
-                ...state,
-                rooms
+                ...roomData,
+                showUsers: false
             };
-        }
+    }
+};
+
+export default (state = initialState, action) => {
+    const { type, payload } = action;
 
+    switch (type) {
+        case SOCKET_RECEIVE_MESSAGE:
+            return reduceReceiveMessage(state, payload);
+
+        case ROOM_JOIN:
+        case ROOM_LEAVE:
+        case ROOM_SHOW_USERS:
         case ROOM_HIDE_USERS:
         {
-            const rooms = state.rooms.set(payload, {
-                ...state.rooms.get(payload),
-                showUsers: false
-            });
+            const roomData = state.roomMap.get(payload);
+            const roomMap = state.roomMap.set(payload,
+                reduceRoom(roomData, action)
+            );
             return {
                 ...state,
-                rooms
+                roomMap
             };
         }
 
+        case ROOM_MESSAGE:
         default:
             return state;
     }