Allow histogram bin bounds to be specified explicitly

Author: milliams

CHANGELOG

@@ -16,6 +16,7 @@
 - Rename `Histogram::from_vec` to `Histogram::from_slice`.
 - Rename `view::View` to `view::ContinuousView` and introduce `view::View` as a trait.
 - Change `svg_render` functions to take data slices rather than Representations.
+- `Histogram::from_slice` now takes either a bin count or a bin bound list as its second argument.
 
 ## 0.3.0 - 2018-03-01
 ### Added

examples/histogram_svg.rs

@@ -4,7 +4,7 @@ use plotlib::style::Bar;
 
 fn main() {
     let data = [0.3, 0.5, 6.4, 5.3, 3.6, 3.6, 3.5, 7.5, 4.0];
-    let h = plotlib::histogram::Histogram::from_slice(&data, 10)
+    let h = plotlib::histogram::Histogram::from_slice(&data, plotlib::histogram::Bins::Count(10))
         .style(plotlib::histogram::Style::new().fill("burlywood"));
     let v = plotlib::view::ContinuousView::new().add(&h);
     plotlib::page::Page::single(&v)

examples/histogram_text.rs

@@ -2,7 +2,7 @@ extern crate plotlib;
 
 fn main() {
     let data = [0.3, 0.5, 6.4, 5.3, 3.6, 3.6, 3.5, 7.5, 4.0];
-    let h = plotlib::histogram::Histogram::from_slice(&data, 10);
+    let h = plotlib::histogram::Histogram::from_slice(&data, plotlib::histogram::Bins::Count(10));
     let v = plotlib::view::ContinuousView::new().add(&h);
     println!("{}", plotlib::page::Page::single(&v).dimensions(60, 15).to_text().unwrap());
 }

src/histogram.rs

@@ -10,7 +10,7 @@ A module for Histograms
 let data = vec![0.3, 0.5, 6.4, 5.3, 3.6, 3.6, 3.5, 7.5, 4.0];
 
 // and create a histogram out of it
-let h = Histogram::from_slice(&data, 30);
+let h = Histogram::from_slice(&data, plotlib::histogram::Bins::Count(30));
 ```
 
 TODO:
@@ -68,6 +68,12 @@ enum HistogramType {
     Density,
 }
 
+#[derive(Debug)]
+pub enum Bins {
+    Count(usize),
+    Bounds(Vec<f64>),
+}
+
 /**
 A one-dimensional histogram with equal binning.
 */
@@ -81,7 +87,7 @@ pub struct Histogram {
 }
 
 impl Histogram {
-    pub fn from_slice(v: &[f64], num_bins: usize) -> Histogram {
+    pub fn from_slice(v: &[f64], bins: Bins) -> Histogram {
         let mut max = v.iter().fold(-1. / 0., |a, &b| f64::max(a, b));
         let mut min = v.iter().fold(1. / 0., |a, &b| f64::min(a, b));
 
@@ -90,18 +96,22 @@ impl Histogram {
             max += 0.5;
         }
 
-        let mut bins = vec![0; num_bins];
+        let (num_bins, bounds) = match bins {
+            Bins::Count(num_bins) => {
+                let range = max - min;
+                let mut bounds: Vec<f64> = (0..num_bins)
+                    .map(|n| (n as f64 / num_bins as f64) * range + min)
+                    .collect();
+                bounds.push(max);
+                (num_bins, bounds)
+            }
+            Bins::Bounds(bounds) => (bounds.len(), bounds),
+        };
 
-        let range = max - min;
+        let mut bins = vec![0; num_bins];
 
         let bin_width = (max - min) / num_bins as f64; // width of bin in real units
 
-        let mut bounds: Vec<f64> = (0..num_bins)
-            .map(|n| (n as f64 / num_bins as f64) * range + min)
-            .collect();
-        bounds.push(max);
-        let bounds = bounds;
-
         for &val in v.iter() {
             /*
             let mut bin = ((val - min) / bin_width) as usize;
@@ -211,15 +221,33 @@ mod tests {
 
     #[test]
     fn test_histogram_from_slice() {
-        assert_eq!(Histogram::from_slice(&[], 3).get_values(), [0., 0., 0.]);
-        assert_eq!(Histogram::from_slice(&[0.], 3).get_values(), [0., 1., 0.]);
         assert_eq!(
-            Histogram::from_slice(&[0., 3.], 3).get_values(),
+            Histogram::from_slice(&[], Bins::Count(3)).get_values(),
+            [0., 0., 0.]
+        );
+        assert_eq!(
+            Histogram::from_slice(&[0.], Bins::Count(3)).get_values(),
+            [0., 1., 0.]
+        );
+        assert_eq!(
+            Histogram::from_slice(&[0., 3.], Bins::Count(3)).get_values(),
             [1., 0., 1.]
         );
         assert_eq!(
-            Histogram::from_slice(&[0., 1., 2., 3.], 3).get_values(),
+            Histogram::from_slice(&[0., 1., 2., 3.], Bins::Count(3)).get_values(),
             [2., 1., 1.]
         );
     }
+
+    #[test]
+    fn test_histogram_define_bin_bounds() {
+        assert_eq!(
+            Histogram::from_slice(&[0., 1.], Bins::Count(3)).bin_bounds,
+            [0., 1. / 3., 2. / 3., 1.]
+        );
+        assert_eq!(
+            Histogram::from_slice(&[], Bins::Bounds([0., 1., 1.5, 2., 5.6].to_vec())).bin_bounds,
+            [0., 1., 1.5, 2., 5.6]
+        );
+    }
 }

src/text_render.rs

@@ -593,7 +593,7 @@ mod tests {
     #[test]
     fn test_render_face_bars() {
         let data = vec![0.3, 0.5, 6.4, 5.3, 3.6, 3.6, 3.5, 7.5, 4.0];
-        let h = histogram::Histogram::from_slice(&data, 10);
+        let h = histogram::Histogram::from_slice(&data, histogram::Bins::Count(10));
         let x_axis = axis::ContinuousAxis::new(0.3, 7.5);
         let y_axis = axis::ContinuousAxis::new(0., 3.);
         let strings = render_face_bars(&h, &x_axis, &y_axis, 20, 10);