histogram: Implement iteration over bin centers

src/traits.rs

@@ -28,6 +28,11 @@ pub trait Histogram:
     fn widths(&self) -> IterWidths<<&Self as IntoIterator>::IntoIter> {
         IterWidths { histogram_iter: self.into_iter() }
     }
+
+    /// Return an iterator over the bin centers.
+    fn centers(&self) -> IterBinCenters<<&Self as IntoIterator>::IntoIter> {
+        IterBinCenters { histogram_iter: self.into_iter() }
+    }
 }
 
 /// Iterate over the bins normalized by bin width.
@@ -65,3 +70,21 @@ impl<T> Iterator for IterWidths<T>
         self.histogram_iter.next().map(|((a, b), _)| b - a)
     }
 }
+
+/// Iterate over the bin centers.
+pub struct IterBinCenters<T>
+    where T: Iterator<Item = ((f64, f64), u64)>
+{
+    histogram_iter: T,
+}
+
+impl<T> Iterator for IterBinCenters<T>
+    where T: Iterator<Item = ((f64, f64), u64)>
+{
+    type Item = f64;
+
+    #[inline]
+    fn next(&mut self) -> Option<f64> {
+        self.histogram_iter.next().map(|((a, b), _)| 0.5 * (a + b))
+    }
+}

tests/histogram.rs

@@ -69,6 +69,18 @@ fn widths() {
     }
 }
 
+#[test]
+fn centers() {
+    let inf = std::f64::INFINITY;
+    let h = Histogram10::from_ranges(
+        [-inf, 0.1, 0.2, 0.3, 0.4, 0.4, 0.7, 0.8, 0.9, 1.0, inf].iter().cloned()).unwrap();
+    let centers: Vec<f64> = h.centers().collect();
+    let expected = [-inf, 0.15, 0.25, 0.35, 0.4, 0.55, 0.75, 0.85, 0.95, inf];
+    for (a, b) in centers.iter().zip(expected.iter()) {
+        assert_almost_eq!(a, b, 1e-14);
+    }
+}
+
 #[test]
 fn from_ranges_infinity() {
     let inf = std::f64::INFINITY;