Set default axis bounds when all values are equal

Fixes #36

Author: milliams

CHANGELOG

@@ -1,6 +1,8 @@
 # Changelog
 
 ## Unreleased
+### Fixed
+- Set default axis bounds for case where all values are equal (Issue #36)
 
 ## 0.5.0 - 2020-03-14
 ### Added

src/utils.rs

@@ -49,6 +49,17 @@ pub fn range(s: &[f64]) -> (f64, f64) {
     (min, max)
 }
 
+/**
+Floor or ceiling the min or max to zero to avoid them both having the same value
+*/
+pub fn pad_range_to_zero(min: f64, max: f64) -> (f64, f64) {
+    if (min - max).abs() < std::f64::EPSILON {
+        (if min > 0. {0.} else {min}, if max < 0. {0.} else {max})
+    } else {
+        (min, max)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -97,4 +108,11 @@ mod tests {
         assert_eq!(quartiles(&[1., 2., 4.]), (1., 2., 4.));
         assert_eq!(quartiles(&[1., 2., 3., 4.]), (1.5, 2.5, 3.5));
     }
+
+    #[test]
+    fn test_pad_range_to_zero() {
+        assert_eq!(pad_range_to_zero(2.0, 2.0), (0.0, 2.0));
+        assert_eq!(pad_range_to_zero(-2.0, 2.0), (-2.0, 2.0));
+        assert_eq!(pad_range_to_zero(-2.0, -2.0), (-2.0, 0.0));
+    }
 }

src/view.rs

@@ -18,6 +18,7 @@ use crate::grid::{Grid, GridType};
 use crate::repr::{CategoricalRepresentation, ContinuousRepresentation};
 use crate::svg_render;
 use crate::text_render;
+use crate::utils;
 
 pub trait View {
     fn to_svg(&self, face_width: f64, face_height: f64) -> Result<svg::node::element::Group>;
@@ -108,6 +109,7 @@ impl ContinuousView {
             x_min = x_min.min(this_x_min);
             x_max = x_max.max(this_x_max);
         }
+        let (x_min, x_max) = utils::pad_range_to_zero(x_min, x_max);
         axis::Range::new(x_min, x_max)
     }
 
@@ -119,6 +121,7 @@ impl ContinuousView {
             y_min = y_min.min(this_y_min);
             y_max = y_max.max(this_y_max);
         }
+        let (y_min, y_max) = utils::pad_range_to_zero(y_min, y_max);
         axis::Range::new(y_min, y_max)
     }