Make ObjectIterator goTo absolute, and add skip function to triples a…

…nd object iterator

hdt-lib/include/Iterator.hpp

@@ -219,6 +219,10 @@ class IteratorTripleID {
 		return false;
 	}
 	virtual void goTo(unsigned int /*pos*/) {
+	/* Absolute repositioning of index: ie. go to the index set in the given argument (pos) */
+	}
+	virtual void skip(unsigned int /*pos*/) {
+	/* Relative repositioning of index: ie. skip index by given argument places */
 	}
 	virtual bool findNextOccurrence(unsigned int /*value*/, unsigned char /*component*/) {
 		return false;

hdt-lib/src/triples/BitmapTriples.hpp

@@ -171,6 +171,7 @@ class BitmapTriplesSearchIterator : public IteratorTripleID {
 	TripleComponentOrder getOrder();
 	bool canGoTo();
 	void goTo(unsigned int pos);
+	void skip(unsigned int pos);
 	bool findNextOccurrence(unsigned int value, unsigned char component);
 	bool isSorted(TripleComponentRole role);
 };
@@ -203,6 +204,7 @@ class MiddleWaveletIterator : public IteratorTripleID {
 	TripleComponentOrder getOrder();
 	bool canGoTo();
 	void goTo(unsigned int pos);
+	void skip(unsigned int pos);
 	bool findNextOccurrence(unsigned int value, unsigned char component);
 	bool isSorted(TripleComponentRole role);
 };
@@ -265,6 +267,7 @@ class ObjectIndexIterator : public IteratorTripleID {
 	TripleComponentOrder getOrder();
 	bool canGoTo();
 	void goTo(unsigned int pos);
+	void skip(unsigned int pos);
 	bool findNextOccurrence(unsigned int value, unsigned char component);
 	bool isSorted(TripleComponentRole role);
 };

hdt-lib/src/triples/BitmapTriplesIterators.cpp

@@ -247,14 +247,26 @@ bool BitmapTriplesSearchIterator::canGoTo() {
     return true;
 }
 
+template <typename T>
+  std::string NumberToString ( T Number )
+  {
+     std::ostringstream ss;
+     ss << Number;
+     return ss.str();
+  }
+
 void BitmapTriplesSearchIterator::goTo(unsigned int pos) {
     if ((pos) >= maxZ) {
-			throw std::runtime_error("Cannot goTo on this pattern.");
+    	throw std::runtime_error(string("Given index is ") + NumberToString(pos) + ". Cannot go beyond last element index: " + NumberToString(maxZ));
 	}
-    posZ = minZ+pos; // move the position of Z
+    posZ = pos; // move the position of Z
 	goToY(); // go to the correct Y
 }
 
+void BitmapTriplesSearchIterator::skip(unsigned int pos) {
+	goTo(posZ+pos);
+}
+
 TripleComponentOrder BitmapTriplesSearchIterator::getOrder() {
     return triples->order;
 }
@@ -439,6 +451,10 @@ void MiddleWaveletIterator::goTo(unsigned int pos) {
     z = adjZ.get(posZ);
 }
 
+void MiddleWaveletIterator::skip(unsigned int pos) {
+   goTo(predicateOcurrence+pos);
+}
+
 size_t MiddleWaveletIterator::estimatedNumResults()
 {
 	if (triples->predicateCount!=NULL){
@@ -902,10 +918,15 @@ bool ObjectIndexIterator::canGoTo()
 
 void ObjectIndexIterator::goTo(unsigned int pos)
 {
-    if(minIndex+pos>maxIndex) {
-	throw std::runtime_error("Cannot goto beyond last element");
+    if(pos>maxIndex) {
+    	throw std::runtime_error(string("Given index: ") + NumberToString(pos) + ". Cannot go beyond last element index: " + NumberToString(maxIndex));
     }
-    posIndex = minIndex+pos;
+    posIndex = pos;
+}
+
+void ObjectIndexIterator::skip(unsigned int pos)
+{
+	goTo(minIndex+pos);
 }
 
 bool ObjectIndexIterator::findNextOccurrence(unsigned int value, unsigned char component) {

hdt-lib/src/triples/TripleIterators.cpp

@@ -155,6 +155,11 @@ void SequentialSearchIteratorTripleID::goTo(unsigned int pos){
 		doFetchNext();
 	}
 }
+void SequentialSearchIteratorTripleID::skip(unsigned int pos){
+	for (int i=0;i<pos;i++){
+		doFetchNext();
+	}
+}
 
 void SequentialSearchIteratorTripleID::doFetchPrevious()
 {

hdt-lib/src/triples/TripleIterators.hpp

@@ -72,6 +72,7 @@ class SequentialSearchIteratorTripleID : public IteratorTripleID {
 	size_t estimatedNumResults();
 	bool canGoTo();
 	void goTo(unsigned int pos);
+	void skip(unsigned int pos);
 
 	bool hasNext();
 	TripleID *next();

hdt-lib/tests/goto.cpp → hdt-lib/tests/randomSolution.cpp

@@ -28,9 +28,9 @@ void signalHandler(int sig) {
 }
 
 void help() {
-	cout << "$ goto <HDT file> <subject> <predicate> <object> " << endl;
+	cout << "$ randomSolution <HDT file> <subject> <predicate> <object> " << endl;
 	cout << "\t-h\t\t\t\tThis help" << endl;
-	cout << "\t-q\t<query>\t\tLaunch query to search for a random solution. E.g. \"? http://www.w3.org/2000/01/rdf-schema#label ?\"" << endl;
+	cout << "\t-q\t<query>\t\tLaunch query and pick a random solution. E.g. \"? http://www.w3.org/2000/01/rdf-schema#label ?\"" << endl;
 }
 
 int main(int argc, char **argv) {
@@ -93,7 +93,7 @@ int main(int argc, char **argv) {
 			int randNumber = int(numResults * rand() / (RAND_MAX));
 			cout << "We pick the random solution #" << randNumber << " out of " << numResults << " results"<< endl;
 
-			it->goTo(randNumber);
+			it->skip(randNumber);
 			TripleID* result=it->next();
 			cout<<"The selected random triple ID is: "<<result->getSubject()<<" "<<result->getPredicate()<<" "<<result->getObject()<<endl;
 			TripleString resString;