added RangeAverage method

Author: Rachel Lin

slidingwindow.go

@@ -93,6 +93,16 @@ func (sw *SlidingWindow) Average(window time.Duration) float64 {
 	return float64(total) / float64(sampleCount)
 }
 
+// RangeAverage returns the unweighted mean of the window
+// from start to end
+func (sw *SlidingWindow) RangeAverage(start, end time.Duration) float64 {
+	total, sampleCount := sw.RangeTotal(start, end)
+	if sampleCount == 0 {
+		return 0
+	}
+	return float64(total) / float64(sampleCount)
+}
+
 // Reset the samples in this sliding time window.
 func (sw *SlidingWindow) Reset() {
 	sw.Lock()
@@ -139,3 +149,30 @@ func (sw *SlidingWindow) Total(window time.Duration) (int64, int) {
 
 	return total, sampleCount
 }
+
+// RangeTotal returns the sum of all values from start to end, as well as
+// the number of samples.
+func (sw *SlidingWindow) RangeTotal(start, end time.Duration) (int64, int) {
+	  if start > end {
+                  start = end
+          }
+	  window := end - start
+	  sampleCount := int(window / sw.granularity)
+          if sampleCount > sw.size {
+                  sampleCount = sw.size
+          }
+	  sw.RLock()
+          defer sw.RUnlock()
+
+          var total int64
+	  endPos := sw.pos - sw.size + int( end / sw.granularity)
+          for i := 1; i <= sampleCount; i++ {
+                  pos := endPos - i
+		  if pos < 0 {
+                          pos += len(sw.samples)
+                  }
+
+                  total += sw.samples[pos]
+          }
+	  return total, sampleCount
+}

slidingwindow_test.go

@@ -19,7 +19,7 @@ func TestNew(t *testing.T) {
 		t.Errorf("expected multiplier error, not %q", err)
 	}
 
-	_, err = New(0, time.Second)
+	_, err = New(0, 5*time.Second)
 	if err == nil || err.Error() != "window cannot be 0" {
 		t.Errorf("expected window size cannot be 0 error, not %q", err)
 	}
@@ -75,6 +75,29 @@ func TestAverage(t *testing.T) {
 	}
 }
 
+func TestRangeAverage(t *testing.T) {
+        sw := &SlidingWindow{
+                window:      10 * time.Second,
+                granularity: time.Second,
+                samples:     []int64{1, 2, 5, 0, 0, 0, 0, 0, 4, 0},
+                pos:         2,
+                size:        10,
+        }
+
+        if v := sw.RangeAverage(0, 0); v != 0 {
+                t.Errorf("expected the average with a window of 0 seconds be 0, not %f", v)
+        }
+        if v := sw.RangeAverage(9 * time.Second, 10 * time.Second); v != 2 {
+                t.Errorf("expected the average from second 9 to 10 to be 2, not %f", v)
+        }
+        if v := sw.RangeAverage(8 * time.Second, 10 * time.Second); v != 1.5 {
+                t.Errorf("expected the average from second 8 to 10 to be 1.5, not %f", v)
+        }
+        if v := sw.RangeAverage(4 * time.Second, 9 * time.Second); v != 1 {
+                t.Errorf("expected the average from second 4 to 9 to be 1, not %f", v)
+        }
+}
+
 func TestReset(t *testing.T) {
 	sw := MustNew(2*time.Second, time.Second)
 	defer sw.Stop()
@@ -131,3 +154,44 @@ func TestTotal(t *testing.T) {
 		t.Errorf("expected the total over the last 10 seconds to be 12, not %d", v)
 	}
 }
+
+func TestRangeTotal(t *testing.T) {
+          sw := &SlidingWindow{
+                  window:      10 * time.Second,
+                  granularity: time.Second,
+                  samples:     []int64{1, 2, 5, 0, 0, 0, 0, 0, 4, 8},
+                  pos:         10,
+                  size:        10,
+          }
+
+          if v, _ := sw.RangeTotal(time.Second, 2 * time.Second); v != 2 {
+                  t.Errorf("expected the total from second 1 to 2 to be 2, not %d", v)
+          }
+	  if v, _ := sw.RangeTotal(time.Second, 3 * time.Second); v != 7 {
+                  t.Errorf("expected the total from second 1 to 3 to be 7, not %d", v)
+          }
+	  if v, _ := sw.RangeTotal(time.Second * 3, time.Second * 8); v != 0 {
+                  t.Errorf("expected the total from second 3 to 8 to be 0, not %d", v)
+          }
+	  if v, _ := sw.RangeTotal(0, time.Second * 2); v != 3 {
+                  t.Errorf("expected the total from second 0 to 2 to be 3, not %d", v)
+          }
+	  if v, _ := sw.RangeTotal(9 * time.Second, 10 * time.Second); v != 8 {
+                  t.Errorf("expected the total from second 9 to 10 to be 8, not %d", v)
+          }
+	
+	  sw = &SlidingWindow{
+                  window:      10 * time.Second,
+                  granularity: time.Second,
+                  samples:     []int64{1, 2, 5, 0, 0, 0, 0, 0, 4, 8},
+                  pos:         2,
+                  size:        10,
+          }
+
+	  if v, _ := sw.RangeTotal(9 * time.Second, 10 * time.Second); v != 2 {
+                  t.Errorf("expected the total from second 9 to 10 to be 2, not %d", v)
+          }
+	  if v, _ := sw.RangeTotal(7 * time.Second, 9 * time.Second); v != 9 {
+                  t.Errorf("expected the total from second 7 to 9 to be 9, not %d", v)
+          }
+}