diff --git a/cpp/LinearFactor.cpp b/cpp/LinearFactor.cpp
index b20a9257b..e0d233e9f 100644
--- a/cpp/LinearFactor.cpp
+++ b/cpp/LinearFactor.cpp
@@ -15,6 +15,7 @@ namespace ublas = boost::numeric::ublas;
 // trick from some reading group
 #define FOREACH_PAIR( KEY, VAL, COL) BOOST_FOREACH (boost::tie(KEY,VAL),COL) 
 
+using namespace std;
 using namespace gtsam;
 
 typedef pair<const string, Matrix>& mypair;
@@ -75,6 +76,15 @@ bool LinearFactor::equals(const Factor& f, double tol) const {
   return false;
 }
 
+/* ************************************************************************* */
+set<string> LinearFactor::keys() const {
+	set<string> result;
+  string j; Matrix A;
+  FOREACH_PAIR(j,A,As)
+    result.insert(j);
+  return result;
+}
+
 /* ************************************************************************* */
 VariableSet LinearFactor::variables() const {
   VariableSet result;
diff --git a/cpp/LinearFactor.h b/cpp/LinearFactor.h
index 47b8b0475..c1ee42b42 100644
--- a/cpp/LinearFactor.h
+++ b/cpp/LinearFactor.h
@@ -144,6 +144,12 @@ public:
 	 */
 	int numberOfRows() const { return b.size();}
 
+	/**
+	 * Find all variables
+	 * @return The set of all variable keys
+	 */
+	std::set<std::string> keys() const;
+
 	/**
 	 * Find all variables and their dimensions
 	 * @return The set of all variable/dimension pairs
diff --git a/cpp/testLinearFactor.cpp b/cpp/testLinearFactor.cpp
index 93f73534c..74abc5d1b 100644
--- a/cpp/testLinearFactor.cpp
+++ b/cpp/testLinearFactor.cpp
@@ -42,6 +42,18 @@ TEST( LinearFactor, linearFactor )
     CHECK( lf->equals(expected) );
 }
 
+/* ************************************************************************* */
+TEST( LinearFactor, keys )
+{
+  // get the factor "f2" from the small linear factor graph
+  LinearFactorGraph fg = createLinearFactorGraph();
+  LinearFactor::shared_ptr lf = fg[1];
+  set<string> expected;
+  expected.insert("x1");
+  expected.insert("x2");
+  CHECK(lf->keys() == expected);
+}
+
 /* ************************************************************************* */
 TEST( LinearFactor, variables )
 {