diff --git a/gtsam/base/DSFVector.cpp b/gtsam/base/DSFVector.cpp
index 0881465ba..42a3bb96c 100644
--- a/gtsam/base/DSFVector.cpp
+++ b/gtsam/base/DSFVector.cpp
@@ -18,6 +18,8 @@
  *               As a result, the size of the forest is prefixed.
  */
 
+#include <boost/make_shared.hpp>
+#include <boost/foreach.hpp>
 #include <gtsam/base/DSFVector.h>
 
 using namespace std;
@@ -26,23 +28,27 @@ namespace gtsam {
 
 	/* ************************************************************************* */
 	DSFVector::DSFVector (const size_t numNodes) {
-		resize(numNodes);
+		v_ = boost::make_shared<V>(numNodes);
 		int index = 0;
-		for(iterator it = begin(); it!=end(); it++, index++)
+		keys_.reserve(numNodes);
+		for(V::iterator it = v_->begin(); it!=v_->end(); it++, index++) {
 			*it = index;
+			keys_.push_back(index);
+		}
 	}
 
 	/* ************************************************************************* */
-	DSFVector::Label DSFVector::findSet(const size_t& key) const {
-		size_t parent = at(key);
-		return parent == key ? key : findSet(parent);
+	DSFVector::DSFVector(const boost::shared_ptr<V>& v_in, const std::vector<size_t>& keys) : keys_(keys) {
+		v_ = v_in;
+		BOOST_FOREACH(const size_t key, keys)
+			(*v_)[key] = key;
 	}
 
 	/* ************************************************************************* */
 	bool DSFVector::isSingleton(const Label& label) const {
 		bool result = false;
-		std::vector<size_t>::const_iterator it = begin();
-		for (; it != end(); ++it) {
+		V::const_iterator it = keys_.begin();
+		for (; it != keys_.end(); ++it) {
 			if(findSet(*it) == label) {
 				if (!result) // find the first occurrence
 					result = true;
@@ -56,11 +62,10 @@ namespace gtsam {
 	/* ************************************************************************* */
 	std::set<size_t> DSFVector::set(const Label& label) const {
 		std::set<size_t> set;
-		size_t key = 0;
-		std::vector<size_t>::const_iterator it = begin();
-		for (; it != end(); it++, key++) {
+		V::const_iterator it = keys_.begin();
+		for (; it != keys_.end(); it++) {
 			if (findSet(*it) == label)
-				set.insert(key);
+				set.insert(*it);
 		}
 		return set;
 	}
@@ -68,17 +73,26 @@ namespace gtsam {
 	/* ************************************************************************* */
 	std::map<DSFVector::Label, std::set<size_t> > DSFVector::sets() const {
 		std::map<Label, std::set<size_t> > sets;
-		size_t key = 0;
-		std::vector<size_t>::const_iterator it = begin();
-		for (; it != end(); it++, key++) {
-			sets[findSet(*it)].insert(key);
+		V::const_iterator it = keys_.begin();
+		for (; it != keys_.end(); it++) {
+			sets[findSet(*it)].insert(*it);
 		}
 		return sets;
 	}
 
+	/* ************************************************************************* */
+	std::map<DSFVector::Label, std::vector<size_t> > DSFVector::arrays() const {
+		std::map<Label, std::vector<size_t> > arrays;
+		V::const_iterator it = keys_.begin();
+		for (; it != keys_.end(); it++) {
+			arrays[findSet(*it)].push_back(*it);
+		}
+		return arrays;
+	}
+
 	/* ************************************************************************* */
 	void DSFVector::makeUnionInPlace(const size_t& i1, const size_t& i2)  {
-		at(findSet(i2)) = findSet(i1);
+		(*v_)[findSet(i2)] = findSet(i1);
 	}
 
 } // namespace
diff --git a/gtsam/base/DSFVector.h b/gtsam/base/DSFVector.h
index 435304ba5..c69582633 100644
--- a/gtsam/base/DSFVector.h
+++ b/gtsam/base/DSFVector.h
@@ -23,23 +23,41 @@
 #include <vector>
 #include <map>
 #include <set>
+#include <boost/shared_ptr.hpp>
 
 namespace gtsam {
 
 	/**
 	 * A fast impelementation of disjoint set forests that uses vector as underly data structure.
 	 */
-	class DSFVector : protected std::vector<std::size_t> {
-	private:
+	class DSFVector {
 
 	public:
+		typedef std::vector<size_t> V;
 		typedef size_t Label;
+		typedef std::vector<size_t>::const_iterator const_iterator;
+		typedef std::vector<size_t>::iterator iterator;
 
-		// constructor
-		DSFVector(const std::size_t numNodes);
+	private:
+		boost::shared_ptr<V> v_; // could use existing memory to improve the efficiency
+		std::vector<size_t> keys_;
+
+	public:
+		// constructor that allocate a new memory
+		DSFVector(const size_t numNodes);
+
+		// constructor that uses the existing memory
+		DSFVector(const boost::shared_ptr<V>& v_in, const std::vector<size_t>& keys);
 
 		// find the label of the set in which {key} lives
-		Label findSet(const size_t& key) const;
+		inline Label findSet(size_t key) const {
+			size_t parent = (*v_)[key];
+			while (parent != key) {
+				key = parent;
+				parent = (*v_)[key];
+			}
+			return parent;
+		}
 
 		// find whether there is one and only one occurrence for the given {label}
 		bool isSingleton(const Label& label) const;
@@ -49,9 +67,10 @@ namespace gtsam {
 
 		// return all sets, i.e. a partition of all elements
 		std::map<Label, std::set<size_t> > sets() const;
+		std::map<Label, std::vector<size_t> > arrays() const;
 
 		// the in-place version of makeUnion
-		void makeUnionInPlace(const std::size_t& i1, const std::size_t& i2);
+		void makeUnionInPlace(const size_t& i1, const size_t& i2);
 
 	};
 
diff --git a/gtsam/base/tests/testDSFVector.cpp b/gtsam/base/tests/testDSFVector.cpp
index ce4ea7f21..81e4f3b07 100644
--- a/gtsam/base/tests/testDSFVector.cpp
+++ b/gtsam/base/tests/testDSFVector.cpp
@@ -18,8 +18,10 @@
  */
 
 #include <iostream>
+#include <boost/make_shared.hpp>
 #include <boost/assign/std/list.hpp>
 #include <boost/assign/std/set.hpp>
+#include <boost/assign/std/vector.hpp>
 using namespace boost::assign;
 #include <CppUnitLite/TestHarness.h>
 
@@ -41,6 +43,15 @@ TEST(DSFVectorVector, makeUnionInPlace) {
 	CHECK(dsf.findSet(0) == dsf.findSet(2));
 }
 
+/* ************************************************************************* */
+TEST(DSFVectorVector, makeUnionInPlace2) {
+	boost::shared_ptr<DSFVector::V> v = boost::make_shared<DSFVector::V>(5);
+	std::vector<size_t> keys; keys += 1, 3;
+	DSFVector dsf(v, keys);
+	dsf.makeUnionInPlace(1,3);
+	CHECK(dsf.findSet(1) == dsf.findSet(3));
+}
+
 /* ************************************************************************* */
 TEST(DSFVector, makeUnion2) {
 	DSFVector dsf(3);
@@ -67,6 +78,17 @@ TEST(DSFVector, sets) {
 	CHECK(expected == sets[dsf.findSet(0)]);
 }
 
+/* ************************************************************************* */
+TEST(DSFVector, arrays) {
+	DSFVector dsf(2);
+	dsf.makeUnionInPlace(0,1);
+	map<size_t, vector<size_t> > arrays = dsf.arrays();
+	LONGS_EQUAL(1, arrays.size());
+
+	vector<size_t> expected; expected += 0, 1;
+	CHECK(expected == arrays[dsf.findSet(0)]);
+}
+
 /* ************************************************************************* */
 TEST(DSFVector, sets2) {
 	DSFVector dsf(3);
@@ -79,6 +101,18 @@ TEST(DSFVector, sets2) {
 	CHECK(expected == sets[dsf.findSet(0)]);
 }
 
+/* ************************************************************************* */
+TEST(DSFVector, arrays2) {
+	DSFVector dsf(3);
+	dsf.makeUnionInPlace(0,1);
+	dsf.makeUnionInPlace(1,2);
+	map<size_t, vector<size_t> > arrays = dsf.arrays();
+	LONGS_EQUAL(1, arrays.size());
+
+	vector<size_t> expected; expected += 0, 1, 2;
+	CHECK(expected == arrays[dsf.findSet(0)]);
+}
+
 /* ************************************************************************* */
 TEST(DSFVector, sets3) {
 	DSFVector dsf(3);
@@ -90,6 +124,17 @@ TEST(DSFVector, sets3) {
 	CHECK(expected == sets[dsf.findSet(0)]);
 }
 
+/* ************************************************************************* */
+TEST(DSFVector, arrays3) {
+	DSFVector dsf(3);
+	dsf.makeUnionInPlace(0,1);
+	map<size_t, vector<size_t> > arrays = dsf.arrays();
+	LONGS_EQUAL(2, arrays.size());
+
+	vector<size_t> expected; expected += 0, 1;
+	CHECK(expected == arrays[dsf.findSet(0)]);
+}
+
 /* ************************************************************************* */
 TEST(DSFVector, set) {
 	DSFVector dsf(3);