add possibility to iterate over SparseVector data at runtime (#143)

matrix/SparseVector.hpp

@@ -60,7 +60,7 @@ private:
     }
 
 public:
-    static constexpr size_t non_zeros() {
+    constexpr size_t non_zeros() const {
         return N;
     }
 
@@ -94,6 +94,16 @@ public:
         return _data[compressed_index];
     }
 
+    inline Type atCompressedIndex(size_t i) const {
+        assert(i < N);
+        return _data[i];
+    }
+
+    inline Type& atCompressedIndex(size_t i) {
+        assert(i < N);
+        return _data[i];
+    }
+
     void setZero() {
         for (size_t i = 0; i < N; i++) {
             _data[i] = Type(0);

test/sparseVector.cpp

@@ -31,6 +31,16 @@ TEST(sparseVectorTest, initialisationFromVector) {
     EXPECT_FLOAT_EQ(a.at<2>(), vec(2));
 }
 
+TEST(sparseVectorTest, accessDataWithCompressedIndices) {
+    const Vector3f vec(1.f, 2.f, 3.f);
+    SparseVectorf<3, 0, 2> a(vec);
+    for (size_t i = 0; i < a.non_zeros(); i++) {
+        a.atCompressedIndex(i) = static_cast<float>(i);
+    }
+    EXPECT_FLOAT_EQ(a.at<0>(), a.atCompressedIndex(0));
+    EXPECT_FLOAT_EQ(a.at<2>(), a.atCompressedIndex(1));
+}
+
 TEST(sparseVectorTest, setZero) {
     const float data[3] = {1.f, 2.f, 3.f};
     SparseVectorf<24, 4, 6, 22> a(data);