Histogram error handling

src/histogram/errors.rs

@@ -15,9 +15,19 @@ impl error::Error for BinNotFound {
     fn description(&self) -> &str {
         "No bin has been found."
     }
+}
+
+#[derive(Debug, Clone)]
+pub struct StrategyError;
+
+impl fmt::Display for StrategyError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "The strategy failed to determine a non-zero bin width.")
+    }
+}
 
-    fn cause(&self) -> Option<&error::Error> {
-        // Generic error, underlying cause isn't tracked.
-        None
+impl error::Error for StrategyError {
+    fn description(&self) -> &str {
+        "The strategy failed to determine a non-zero bin width."
     }
 }

src/histogram/grid.rs

@@ -54,7 +54,7 @@ use std::ops::Range;
 ///
 /// // The optimal grid layout is inferred from the data,
 /// // specifying a strategy (Auto in this case)
-/// let grid = GridBuilder::<Auto<usize>>::from_array(&observations).build();
+/// let grid = GridBuilder::<Auto<usize>>::from_array(&observations).unwrap().build();
 /// let expected_grid = Grid::from(vec![Bins::new(Edges::from(vec![1, 20, 39, 58, 77, 96, 115]))]);
 /// assert_eq!(grid, expected_grid);
 ///
@@ -169,17 +169,23 @@ where
     /// it returns a `GridBuilder` instance that has learned the required parameter
     /// to build a [`Grid`] according to the specified [`strategy`].
     ///
+    /// It returns `None` if it is not possible to build a [`Grid`] given
+    /// the observed data according to the chosen [`strategy`].
+    ///
     /// [`Grid`]: struct.Grid.html
     /// [`strategy`]: strategies/index.html
-    pub fn from_array<S>(array: &ArrayBase<S, Ix2>) -> Self
+    pub fn from_array<S>(array: &ArrayBase<S, Ix2>) -> Option<Self>
     where
         S: Data<Elem = A>,
     {
-        let bin_builders = array
+        let bin_builders: Option<Vec<B>> = array
             .axis_iter(Axis(1))
-            .map(|data| B::from_array(&data))
+            .map(|data| match B::from_array(&data) {
+                Ok(Some(builder)) => Some(builder),
+                _ => None,
+            })
             .collect();
-        Self { bin_builders }
+        bin_builders.map(|b| Self { bin_builders: b })
     }
 
     /// Returns a [`Grid`] instance, built accordingly to the specified [`strategy`]

src/histogram/histograms.rs

@@ -123,7 +123,7 @@ where
     ///     [n64(-1.), n64(-0.5)],
     ///     [n64(0.5), n64(-1.)]
     /// ];
-    /// let grid = GridBuilder::<Sqrt<N64>>::from_array(&observations).build();
+    /// let grid = GridBuilder::<Sqrt<N64>>::from_array(&observations).unwrap().build();
     /// let expected_grid = Grid::from(
     ///     vec![
     ///         Bins::new(Edges::from(vec![n64(-1.), n64(0.), n64(1.), n64(2.)])),