diff -r feb7974cf4ec -r 2025a571895e lemon/graph_writer.h
--- a/lemon/graph_writer.h	Tue Aug 28 13:58:54 2007 +0000
+++ b/lemon/graph_writer.h	Tue Aug 28 14:00:42 2007 +0000
@@ -251,9 +251,17 @@
       writer->run();
     }
 
+    /// \brief Returns true if the writer can give back the labels by the items.
+    ///
+    /// Returns true if the writer can give back the the labels by the items.
+    bool isLabelWriter() const {
+      return nodeset_writer.isLabelWriter() && 
+        edgeset_writer.isLabelWriter();
+    }
+
     /// \brief Write the label of the given node.
     ///
-    /// It writes the label of the given node. If there was written an "label"
+    /// It writes the label of the given node. If there was written a "label"
     /// named node map then it will write the map value belonging to the node.
     void writeLabel(std::ostream& os, const Node& item) const {
       nodeset_writer.writeLabel(os, item);
@@ -261,12 +269,32 @@
 
     /// \brief Write the label of the given edge.
     ///
-    /// It writes the label of the given edge. If there was written an "label"
+    /// It writes the label of the given edge. If there was written a "label"
     /// named edge map then it will write the map value belonging to the edge.
     void writeLabel(std::ostream& os, const Edge& item) const {
       edgeset_writer.writeLabel(os, item);
     } 
 
+    /// \brief Sorts the given node vector by label.
+    ///
+    /// Sorts the given node vector by label. If there was written an
+    /// "label" named map then the vector will be sorted by the values
+    /// of this map. Otherwise if the \c forceLabel parameter was true
+    /// it will be sorted by its id in the graph.
+    void sortByLabel(std::vector<Node>& nodes) const {
+      nodeset_writer.sortByLabel(nodes);
+    }
+
+    /// \brief Sorts the given edge vector by label.
+    ///
+    /// Sorts the given edge vector by label. If there was written an
+    /// "label" named map then the vector will be sorted by the values
+    /// of this map. Otherwise if the \c forceLabel parameter was true
+    /// it will be sorted by its id in the graph.
+    void sortByLabel(std::vector<Edge>& edges) const {
+      edgeset_writer.sortByLabel(edges);
+    }
+
   private:
 
     LemonWriter* writer;
@@ -370,9 +398,9 @@
     UGraphWriter(std::ostream& _os, const Graph& _graph) 
       : writer(new LemonWriter(_os)), own_writer(true), 
 	nodeset_writer(*writer, _graph, std::string()),
-	u_edgeset_writer(*writer, _graph, nodeset_writer, std::string()),
+	uedgeset_writer(*writer, _graph, nodeset_writer, std::string()),
 	node_writer(*writer, nodeset_writer, std::string()),
-	u_edge_writer(*writer, u_edgeset_writer, std::string()),
+	uedge_writer(*writer, uedgeset_writer, std::string()),
 	attribute_writer(*writer, std::string()) {}
 
     /// \brief Construct a new UGraphWriter.
@@ -382,21 +410,21 @@
     UGraphWriter(const std::string& _filename, const Graph& _graph) 
       : writer(new LemonWriter(_filename)), own_writer(true), 
 	nodeset_writer(*writer, _graph, std::string()),
-	u_edgeset_writer(*writer, _graph, nodeset_writer, std::string()),
+	uedgeset_writer(*writer, _graph, nodeset_writer, std::string()),
 	node_writer(*writer, nodeset_writer, std::string()),
-	u_edge_writer(*writer, u_edgeset_writer, std::string()),
+	uedge_writer(*writer, uedgeset_writer, std::string()),
 	attribute_writer(*writer, std::string()) {}
 
     /// \brief Construct a new UGraphWriter.
     ///
     /// Construct a new UGraphWriter. It writes the given graph
-    /// to given LemonReader.
+    /// to given LemonWriter.
     UGraphWriter(LemonWriter& _writer, const Graph& _graph)
       : writer(_writer), own_writer(false), 
 	nodeset_writer(*writer, _graph, std::string()),
-	u_edgeset_writer(*writer, _graph, nodeset_writer, std::string()),
+	uedgeset_writer(*writer, _graph, nodeset_writer, std::string()),
 	node_writer(*writer, nodeset_writer, std::string()),
-	u_edge_writer(*writer, u_edgeset_writer, std::string()),
+	uedge_writer(*writer, uedgeset_writer, std::string()),
 	attribute_writer(*writer, std::string()) {}
 
     /// \brief Destruct the graph writer.
@@ -434,7 +462,7 @@
     /// the writer.
     template <typename Map>
     UGraphWriter& writeEdgeMap(std::string label, const Map& map) { 
-      u_edgeset_writer.writeEdgeMap(label, map);
+      uedgeset_writer.writeEdgeMap(label, map);
       return *this;
     }
 
@@ -445,7 +473,7 @@
     template <typename ItemWriter, typename Map>
     UGraphWriter& writeEdgeMap(std::string label, const Map& map,
 				   const ItemWriter& iw = ItemWriter()) {
-      u_edgeset_writer.writeEdgeMap(label, map, iw);
+      uedgeset_writer.writeEdgeMap(label, map, iw);
       return *this;
     }
 
@@ -455,7 +483,7 @@
     /// command</i> to the writer.
     template <typename Map>
     UGraphWriter& writeUEdgeMap(std::string label, const Map& map) { 
-      u_edgeset_writer.writeUEdgeMap(label, map);
+      uedgeset_writer.writeUEdgeMap(label, map);
       return *this;
     }
 
@@ -466,7 +494,7 @@
    template <typename ItemWriter, typename Map>
     UGraphWriter& writeUEdgeMap(std::string label, const Map& map,
 					const ItemWriter& iw = ItemWriter()) {
-      u_edgeset_writer.writeUEdgeMap(label, map, iw);
+      uedgeset_writer.writeUEdgeMap(label, map, iw);
       return *this;
     }
 
@@ -484,7 +512,7 @@
     /// This function issues a new <i> labeled edge writing
     /// command</i> to the writer.
     UGraphWriter& writeEdge(std::string label, const Edge& edge) {
-      u_edge_writer.writeEdge(label, edge);
+      uedge_writer.writeEdge(label, edge);
     }
 
     /// \brief Issue a new labeled undirected edge writing command to
@@ -493,7 +521,7 @@
     /// Issue a new <i>labeled undirected edge writing command</i> to
     /// the writer.
     UGraphWriter& writeUEdge(std::string label, const UEdge& edge) {
-      u_edge_writer.writeUEdge(label, edge);
+      uedge_writer.writeUEdge(label, edge);
     }
 
     /// \brief Issue a new attribute writing command.
@@ -534,9 +562,17 @@
       writer->run();
     }
 
+    /// \brief Returns true if the writer can give back the labels by the items.
+    ///
+    /// Returns true if the writer can give back the the labels by the items.
+    bool isLabelWriter() const {
+      return nodeset_writer.isLabelWriter() && 
+        uedgeset_writer.isLabelWriter();
+    }
+
     /// \brief Write the label of the given node.
     ///
-    /// It writes the label of the given node. If there was written an "label"
+    /// It writes the label of the given node. If there was written a "label"
     /// named node map then it will write the map value belonging to the node.
     void writeLabel(std::ostream& os, const Node& item) const {
       nodeset_writer.writeLabel(os, item);
@@ -544,21 +580,50 @@
 
     /// \brief Write the label of the given edge.
     ///
-    /// It writes the label of the given edge. If there was written an "label"
+    /// It writes the label of the given edge. If there was written a "label"
     /// named edge map then it will write the map value belonging to the edge.
     void writeLabel(std::ostream& os, const Edge& item) const {
-      u_edgeset_writer.writeLabel(os, item);
+      uedgeset_writer.writeLabel(os, item);
     } 
 
     /// \brief Write the label of the given undirected edge.
     ///
     /// It writes the label of the given undirected edge. If there was
-    /// written an "label" named edge map then it will write the map
+    /// written a "label" named edge map then it will write the map
     /// value belonging to the edge.
     void writeLabel(std::ostream& os, const UEdge& item) const {
-      u_edgeset_writer.writeLabel(os, item);
+      uedgeset_writer.writeLabel(os, item);
     } 
 
+    /// \brief Sorts the given node vector by label.
+    ///
+    /// Sorts the given node vector by label. If there was written an
+    /// "label" named map then the vector will be sorted by the values
+    /// of this map. Otherwise if the \c forceLabel parameter was true
+    /// it will be sorted by its id in the graph.
+    void sortByLabel(std::vector<Node>& nodes) const {
+      nodeset_writer.sortByLabel(nodes);
+    }
+
+    /// \brief Sorts the given edge vector by label.
+    ///
+    /// Sorts the given edge vector by label. If there was written an
+    /// "label" named map then the vector will be sorted by the values
+    /// of this map. Otherwise if the \c forceLabel parameter was true
+    /// it will be sorted by its id in the graph.
+    void sortByLabel(std::vector<Edge>& edges) const {
+      uedgeset_writer.sortByLabel(edges);
+    }
+
+    /// \brief Sorts the given undirected edge vector by label.
+    ///
+    /// Sorts the given undirected edge vector by label. If there was
+    /// written an "label" named map then the vector will be sorted by
+    /// the values of this map. Otherwise if the \c forceLabel
+    /// parameter was true it will be sorted by its id in the graph.
+    void sortByLabel(std::vector<UEdge>& uedges) const {
+      uedgeset_writer.sortByLabel(uedges);
+    }
 
   private:
 
@@ -566,10 +631,10 @@
     bool own_writer;
 
     NodeSetWriter<Graph, WriterTraits> nodeset_writer;
-    UEdgeSetWriter<Graph, WriterTraits> u_edgeset_writer;
+    UEdgeSetWriter<Graph, WriterTraits> uedgeset_writer;
 
     NodeWriter<Graph> node_writer;
-    UEdgeWriter<Graph> u_edge_writer;
+    UEdgeWriter<Graph> uedge_writer;
     
     AttributeWriter<WriterTraits> attribute_writer;
   };