Now update MovingMedian behaviour to match bsq code (i.e. make it "more" correct)

src/common/HistogramFilter.h

@@ -44,8 +44,8 @@ class HistogramFilter
 public:
     HistogramFilter(int nValues, int filterLength) :
         m_buffer(filterLength),
-        m_histogram(nValues, 0) {
+        m_histogram(nValues, 0),
-    }
+        m_mode(-1) { }
     ~HistogramFilter() { }
 
     int getFilterLength() const {
@@ -65,13 +65,21 @@ public:
             --m_histogram[toDrop];
         }
         m_buffer.writeOne(value);
-        ++m_histogram[value];
+        int height = ++m_histogram[value];
+        if (m_mode >= 0 && height >= m_histogram[m_mode]) {
+            if (height > m_histogram[m_mode] || value < m_mode) {
+                m_mode = value;
+            }
+        }
     }
 
     void drop() {
         if (m_buffer.getReadSpace() > 0) {
             int toDrop = m_buffer.readOne();
             --m_histogram[toDrop];
+            if (toDrop == m_mode) {
+                m_mode = -1;
+            }
         }
     }
 
@@ -95,6 +103,9 @@ public:
      *  an equal number of times, return the smallest of them.
      */
     int getMode() const {
+        if (m_mode >= 0) {
+            return m_mode;
+        }
         int max = 0;
         int mode = 0;
         for (int i = 0; i < m_histogram.size(); ++i) {
@@ -104,6 +115,7 @@ public:
                 mode = i;
             }
         }
+        m_mode = mode;
         return mode;
     }
 
@@ -168,7 +180,7 @@ public:
 private:
     SingleThreadRingBuffer<int> m_buffer;
     std::vector<int> m_histogram;
-    int m_mode;
+    mutable int m_mode;
 };
 
 }

src/common/MovingMedian.h

@@ -37,19 +37,27 @@
 namespace RubberBand
 {
 
+/**
+ * A median or modal filter implemented using sorting, for continuous
+ * values. Pushing a value updates the sorted record, after which you
+ * can get() the median.  You can call drop() to drop the oldest value
+ * without pushing a new one, for example to drain the filter at the
+ * tail of the sequence.
+ */
 template <typename T>
 class MovingMedian : public SampleFilter<T>
 {
-public:
+    static constexpr float fifty = 50.f;
-    MovingMedian(int filterLength, float percentile = 50.f) :
-        m_buffer(filterLength),
-        m_sortspace(filterLength, {})
-    {
-        setPercentile(percentile);
-    }
     
-    ~MovingMedian() { 
+public:
-    }
+    MovingMedian(int filterLength, float percentile = fifty) :
+        m_buffer(filterLength),
+        m_sortspace(filterLength, {}),
+        m_fill(0),
+        m_percentile(percentile)
+    { }
+
+    ~MovingMedian() { }
 
     MovingMedian(const MovingMedian &) =default;
     MovingMedian &operator=(const MovingMedian &) =default;
@@ -59,10 +67,7 @@ public:
     }
 
     void setPercentile(float p) {
-        int length = getSize();
+        m_percentile = p;
-        m_index = int((length * p) / 100.f);
-        if (m_index >= length) m_index = length-1;
-        if (m_index < 0) m_index = 0;
     }
     
     void push(T value) {
@@ -70,18 +75,34 @@ public:
             std::cerr << "WARNING: MovingMedian: NaN encountered" << std::endl;
             value = T();
         }
-        if (m_buffer.getWriteSpace() == 0) {
+        if (m_fill == getSize()) {
             T toDrop = m_buffer.readOne();
             dropAndPut(toDrop, value);
-            m_buffer.writeOne(value);
         } else {
             put(value);
-            m_buffer.writeOne(value);
+        }
+        m_buffer.writeOne(value);
+    }
+
+    void drop() {
+        if (m_fill > 0) {
+            T toDrop = m_buffer.readOne();
+            drop(toDrop);
         }
     }
     
+    /** Return the median of the values in the filter currently. If
+     *  the median lies between two values, return the first of them.
+     */
     T get() const {
-	return m_sortspace[m_index];
+        int n = m_fill - 1;
+        if (m_percentile == fifty) { // exact default value
+            return m_sortspace[n / 2];
+        } else {
+            int index = float(n) * m_percentile / 100.f;
+            if (index >= m_fill) index = m_fill - 1;
+            return m_sortspace[index];
+        }
     }
 
     void reset() {
@@ -93,26 +114,22 @@ public:
     // in-place. Array has length n. Modifies both the filter and the
     // array.
     //
-    static void filter(MovingMedian<T> &mm, T *v, int n) {
+    static void filter(MovingMedian<T> &f, T *v, int n) {
-        int fn = mm.getSize();
+        f.reset();
-        int lag = fn / 2;
+        int flen = f.getSize();
-        mm.reset();
+        int i = -(flen / 2);
-        int i = 0;
+        int j = 0;
-        for (; i < lag; ++i) {
+        while (i != n) {
-            if (i < n) mm.push(v[i]);
+            if (j < n) {
-        }
+                f.push(v[j]);
-        for (; i < n; ++i) {
+            } else if (j >= flen) {
-            mm.push(v[i]);
+                f.drop();
-            v[i-lag] = mm.get();
+            }
-        }
+            if (i >= 0) {
-        for (; i < lag; ++i) {
+                v[i] = f.get();
-            // just for the unusual case where lag > n
+            }
-            mm.push(T());
+            ++i;
-            (void)mm.get();
+            ++j;
-        }
-        for (; i < n + lag; ++i) {
-            mm.push(T());
-            v[i-lag] = mm.get();
         }
     }
 
@@ -125,18 +142,26 @@ public:
 private:
     SingleThreadRingBuffer<T> m_buffer;
     std::vector<T> m_sortspace;
-    int m_index;
+    int m_fill;
+    float m_percentile;
 
     void dropAndPut(const T &toDrop, const T &toPut) {
-	// precondition: sorted contains m_length values, one of which is toDrop
+	// precondition: sorted contains getSize values, one of which is toDrop
-	// postcondition: sorted contains m_length values, one of which is toPut
+	// postcondition: sorted contains getSize values, one of which is toPut
         // (and one instance of toDrop has been removed)
 
         // This implementation was timed for rather short filters (no
         // longer than maybe 16 items). Two binary searches plus a
         // memmove should be faster for longer ones.
         
-        const int n = getSize();
+        const int n = m_fill;
+
+#ifdef DEBUG_MM
+        if (n != getSize()) {
+            throw std::logic_error("length mismatch");
+        }
+#endif
+        
         T *sorted = m_sortspace.data();
         int dropIx;
         if (toDrop <= *sorted) {
@@ -158,7 +183,7 @@ private:
         std::cout << "toDrop = " << toDrop << ", dropIx = " << dropIx << std::endl;
         std::cout << "toPut = " << toPut << std::endl;
         if (sorted[dropIx] != toDrop) {
-            throw std::logic_error("element not found");
+            throw std::logic_error("element not found (a)");
         }
 #endif
         
@@ -198,14 +223,15 @@ private:
     }
 
     void put(const T &toPut) {
-	// precondition: sorted contains fewer than m_length values,
+	// precondition: sorted contains m_fill values, m_fill < m_length,
 	// packed at the start
-	// postcondition: sorted contains up to m_length values,
+	// postcondition: m_fill is incremented, sorted contains m_fill values,
         // packed at the start, one of which is toPut
-        const int n = m_buffer.getReadSpace(); // items in sorted
+
+        int n = m_fill;
 
 #ifdef DEBUG_MM
-        if (n >= m_length) {
+        if (n >= getSize()) {
             throw std::logic_error("length mismatch");
         }
 #endif
@@ -229,27 +255,81 @@ private:
         }
         sorted[putIx] = toPut;
 
+        ++m_fill;
+
 #ifdef DEBUG_MM
         std::cout << "after: [";
-        for (int i = 0; i < n + 1; ++i) {
+        for (int i = 0; i < m_fill; ++i) {
             if (i > 0) std::cout << ",";
             std::cout << sorted[i];
         }
         std::cout << "]" << std::endl;
 
-        if (!std::is_sorted(sorted, sorted + n)) {
+        if (!std::is_sorted(sorted, sorted + m_fill)) {
             throw std::logic_error("array is not sorted");
         }
 #endif
     }
+
+    void drop(const T &toDrop) {
+	// precondition: sorted contains m_fill values, m_fill > 0, <= m_length,
+	// packed at the start, one of which is toDrop
+	// postcondition: m_fill decremented, sorted contains m_fill values,
+        // packed at the start, none of which is toDrop
+
+        int n = m_fill;
+
+#ifdef DEBUG_MM
+        if (n <= 0 || n > getSize()) {
+            throw std::logic_error("length mismatch");
+        }
+#endif
+            
+        T *sorted = m_sortspace.data();
+        int dropIx = std::lower_bound(sorted, sorted + n, toDrop) - sorted;
+
+#ifdef DEBUG_MM
+        std::cout << "\nbefore: [";
+        for (int i = 0; i < n; ++i) {
+            if (i > 0) std::cout << ",";
+            std::cout << sorted[i];
+        }
+        std::cout << "]" << std::endl;
+
+        std::cout << "toDrop = " << toDrop << ", dropIx = " << dropIx << std::endl;
+        if (sorted[dropIx] != toDrop) {
+            throw std::logic_error("element not found (b)");
+        }
+#endif
+
+        if (dropIx < n - 1) {
+            v_move(sorted + dropIx, sorted + dropIx + 1, n - dropIx - 1);
+        }
+
+        --m_fill;
+        
+#ifdef DEBUG_MM
+        std::cout << "after: [";
+        for (int i = 0; i < m_fill; ++i) {
+            if (i > 0) std::cout << ",";
+            std::cout << sorted[i];
+        }
+        std::cout << "]" << std::endl;
+
+        if (!std::is_sorted(sorted, sorted + m_fill)) {
+            throw std::logic_error("array is not sorted");
+        }
+#endif
+    }
+
 };
 
 template <typename T>
 class MovingMedianStack
 {
 public:
-    MovingMedianStack(int nfilters, int size, float percentile = 50.f) :
+    MovingMedianStack(int nfilters, int size) :
-        m_stack(nfilters, { size, percentile })
+        m_stack(nfilters, { size })
     {
     }
 
@@ -260,12 +340,6 @@ public:
         return m_stack[0].getSize();
     }
 
-    void setPercentile(float p) {
-        for (auto &f: m_stack) {
-            f.setPercentile(p);
-        }
-    }
-
     void push(int filter, T value) {
         m_stack[filter].push(value);
     }

src/test/TestSignalBits.cpp

@@ -34,13 +34,6 @@ namespace tt = boost::test_tools;
 
 BOOST_AUTO_TEST_SUITE(TestSignalBits)
 
-// NB our moving median has different lag behaviour from bsq - we
-// begin padded with zeros, while bsq begins with an empty vector. The
-// bsq behaviour is imho more correct, and this really shows up in the
-// n_1 case below (where the correct answer is surely {1.0} rather
-// than {0.0}) but ours is not wholly wrong, more efficient, "usually
-// fine"
-
 BOOST_AUTO_TEST_CASE(moving_median_simple_3)
 {
     MovingMedian<double> mm(3);
@@ -54,7 +47,7 @@ BOOST_AUTO_TEST_CASE(moving_median_simple_4)
 {
     MovingMedian<double> mm(4);
     vector<double> arr { 1.0, 2.0, 3.0, 4.0 };
-    vector<double> expected { 2.0, 3.0, 3.0, 3.0 };
+    vector<double> expected { 2.0, 2.0, 3.0, 3.0 };
     MovingMedian<double>::filter(mm, arr);
     BOOST_TEST(arr == expected, tt::per_element());
 }
@@ -72,7 +65,7 @@ BOOST_AUTO_TEST_CASE(moving_median_simple_5_4)
 {
     MovingMedian<double> mm(5);
     vector<double> arr { 1.2, 0.6, 1.0e-6, 1.0 };
-    vector<double> expected { 1.0e-6, 0.6, 0.6, 1.0e-6 };
+    vector<double> expected { 0.6, 0.6, 0.6, 0.6 };
     MovingMedian<double>::filter(mm, arr);
     BOOST_TEST(arr == expected, tt::per_element());
 }
@@ -90,7 +83,7 @@ BOOST_AUTO_TEST_CASE(moving_median_n_1)
 {
     MovingMedian<double> mm(6);
     vector<double> arr { 1.0 };
-    vector<double> expected { 0.0 };
+    vector<double> expected { 1.0 };
     MovingMedian<double>::filter(mm, arr);
     BOOST_TEST(arr == expected, tt::per_element());
 }