Histogram error handling

src/histogram/grid.rs

@@ -54,7 +54,7 @@ use ndarray::{ArrayBase, Data, Ix1, Ix2, Axis};
 ///
 /// // 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);
 ///
@@ -160,17 +160,20 @@ 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))
             .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 @@ pub trait HistogramExt<A, S>
     ///     [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.)])),