Implement SGVector slicing

src/shogun/lib/SGMatrix.cpp

@@ -394,7 +394,7 @@ void SGMatrix<T>::create_diagonal_matrix(T* matrix, T* v,int32_t size)
 }
 
 template <class T>
-SGMatrix<T> SGMatrix<T>::submatrix(index_t col_start, index_t col_end) const
+SGMatrix<T> SGMatrix<T>::slice(index_t col_start, index_t col_end) const
 {
 	assert_on_cpu();
 	return SGMatrix<T>(

src/shogun/lib/SGMatrix.h

@@ -151,7 +151,7 @@ template<class T> class SGMatrix : public SGReferencedData
 		 * @param col_end column index (excluded)
 		 * @return the submatrix
 		 */
-		SGMatrix<T> submatrix(index_t col_start, index_t col_end) const;
+		SGMatrix<T> slice(index_t col_start, index_t col_end) const;
 
 		/** Map a column to a SGVector
 		 * \warning The returned SGVector is non-owning!

src/shogun/lib/SGVector.cpp

@@ -309,6 +309,15 @@ void SGVector<T>::resize_vector(int32_t n)
 	vlen=n;
 }
 
+template <class T>
+SGVector<T> SGVector<T>::slice(index_t l, index_t h) const
+{
+	assert_on_cpu();
+	ASSERT(l >= 0 && h <= vlen);
+
+	return SGVector<T>(vector, h - l, l);
+}
+
 /** addition operator */
 template<class T>
 SGVector<T> SGVector<T>::operator+ (SGVector<T> x)

src/shogun/lib/SGVector.h

@@ -270,6 +270,13 @@ template<class T> class SGVector : public SGReferencedData
 		 */
 		void resize_vector(int32_t n);
 
+		/** Returns a view of the vector from l inclusive to h exclusive
+		 *
+		 * @param l slice start index (inclusive)
+		 * @param h slice end index (exclusive)
+		 */
+		SGVector<T> slice(index_t l, index_t h) const;
+
 		/** Operator overload for vector read only access
 		 *
 		 * @param index dimension to access

src/shogun/multiclass/QDA.cpp

@@ -144,7 +144,7 @@ CMulticlassLabels* CQDA::apply_multiclass(CFeatures* data)
 			rf->free_feature_vector(vec, i);
 		}
 
-		Map<MatrixXd> Em_M(m_M.submatrix(m_dim * k, m_dim * (k + 1)));
+		Map<MatrixXd> Em_M(m_M.slice(m_dim * k, m_dim * (k + 1)));
 		A = X*Em_M;
 
 		for (int i = 0; i < num_vecs; i++)

tests/unit/lib/SGMatrix_unittest.cc

@@ -636,7 +636,7 @@ TEST(SGMatrixTest, max_single)
 		EXPECT_GE(max, mat.matrix[i]);
 }
 
-TEST(SGMatrixTest, get_submatrix)
+TEST(SGMatrixTest, get_slice)
 {
 	const index_t n_rows = 6, n_cols = 8;
 	const index_t start_col = 2, end_col = 5;
@@ -646,7 +646,7 @@ TEST(SGMatrixTest, get_submatrix)
 	for (index_t i = 0; i < n_rows * n_cols; ++i)
 		mat[i] = CMath::randn_double();
 
-	auto sub = mat.submatrix(start_col, end_col);
+	auto sub = mat.slice(start_col, end_col);
 
 	EXPECT_EQ(sub.num_rows, mat.num_rows);
 	EXPECT_EQ(sub.num_cols, end_col - start_col);

tests/unit/lib/SGVector_unittest.cc

@@ -468,3 +468,46 @@ TEST(SGVectorTest, as)
 		EXPECT_EQ((int32_t)data[i], vec_int[i]);
 	}
 }
+
+TEST(SGVectorTest, slice)
+{
+	index_t vlen = 100;
+	index_t l = 20;
+	index_t h = 50;
+	index_t l2 = 10;
+	index_t h2 = 20;
+	index_t c1 = 0;
+	index_t c2 = 1;
+
+	SGVector<float64_t> vec(vlen);
+	vec.range_fill();
+
+	auto sliced_vec = vec.slice(l, h);
+	EXPECT_EQ(sliced_vec.size(), h - l);
+	for (index_t i = 0; i < h - l; i++)
+	{
+		EXPECT_EQ(vec[i + l], sliced_vec[i]);
+	}
+
+	auto sliced_vec2 = sliced_vec.slice(l2, h2);
+	EXPECT_EQ(sliced_vec2.size(), h2 - l2);
+	for (index_t i = 0; i < h2 - l2; i++)
+	{
+		EXPECT_EQ(sliced_vec[i + l2], sliced_vec2[i]);
+	}
+
+	sliced_vec.set_const(c1);
+	auto sliced_vec3 = sliced_vec2.slice(0, sliced_vec2.vlen);
+	EXPECT_EQ(sliced_vec2, sliced_vec3);
+	sliced_vec3.set_const(c2);
+
+	for (index_t i = 0; i < vlen; i++)
+	{
+		if (i < l || i >= h)
+			EXPECT_EQ(vec[i], i);
+		else if (i < l + l2 || i >= l + h2)
+			EXPECT_EQ(vec[i], sliced_vec[i - l]);
+		else
+			EXPECT_EQ(vec[i], sliced_vec2[i - l - l2]);
+	}
+}