remove method to set factor to NULL

cpp/FactorGraph-inl.h

@@ -245,7 +245,7 @@ FactorGraph<Factor>::findAndRemoveFactors(const string& key) {
 	BOOST_FOREACH(int i, *indices_ptr) {
 		if(factors_[i] == NULL) continue; // skip NULL factors
 		found.push_back(factors_[i]);     // add to found
-		factors_[i].reset();              // set factor to NULL.
+		remove(i);                        // set factor to NULL.
 	}
 	return found;
 }

cpp/FactorGraph.h

@@ -67,6 +67,9 @@ namespace gtsam {
 		/** Get a specific factor by index */
 		inline sharedFactor operator[](size_t i) const {return factors_[i];}
 
+		/** delete factor without re-arranging indexes by inserting a NULL pointer */
+		inline void remove(size_t i) { factors_[i].reset();}
+
 		/** return the number of factors and NULLS */
 		inline size_t size() const { return factors_.size();}