Switch to a slower but more extensible binning strategy

Author: milliams

src/histogram.rs

@@ -21,6 +21,7 @@ TODO:
 */
 
 use axis;
+use utils::PairWise;
 
 #[derive(Debug)]
 pub struct Histogram {
@@ -51,11 +52,15 @@ impl Histogram {
         let bounds = bounds;
 
         for &val in v.iter() {
+            /*
             let mut bin = ((val - min) / bin_width) as usize;
             if bin == num_bins && val == max {
                 //We are right on the top-most bound
                 bin = num_bins - 1;
             }
+            */
+
+            let bin = bounds.pairwise().enumerate().skip_while(|&(_, (&l, &u))| !(val >= l && val <= u)).map(|(i, (_,_))| i).next().unwrap();
             bins[bin] += 1;
         }
         let density_per_bin = bins.iter().map(|&x| x as f64 / bin_width).collect();

src/lib.rs

@@ -6,3 +6,4 @@ Data structures and helpers for managing plotting data
 
 pub mod histogram;
 pub mod axis;
+pub mod utils;

src/utils.rs

@@ -0,0 +1,36 @@
+use std::iter::{Zip, Skip};
+use std::slice::Iter;
+
+pub trait PairWise<T> {
+    fn pairwise(&self) -> Zip<Iter<T>, Skip<Iter<T>>>;
+}
+
+impl<T> PairWise<T> for [T] {
+    fn pairwise(&self) -> Zip<Iter<T>, Skip<Iter<T>>> {
+        self.iter().zip(self.iter().skip(1))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_pairwise() {
+        let a = [1, 2, 3, 4, 5];
+        assert_eq!(a.pairwise().nth(0).unwrap(), (&1, &2));
+        assert_eq!(a.pairwise().last().unwrap(), (&4, &5));
+        assert_eq!(a.pairwise().len(), a.len() - 1);
+
+        let a = [1, 2];
+        assert_eq!(a.pairwise().nth(0).unwrap(), (&1, &2));
+        assert_eq!(a.pairwise().last().unwrap(), (&1, &2));
+        assert_eq!(a.pairwise().len(), a.len() - 1);
+
+        let a = [1];
+        assert!(a.pairwise().nth(0).is_none());
+
+        let b: Vec<f64> = vec![0.0, 0.1, 0.2];
+        assert_eq!(b.pairwise().nth(0).unwrap(), (&0.0, &0.1));
+    }
+}