implement partialord min/max

src/numeric/impl_numeric.rs

@@ -46,6 +46,84 @@ impl<A, S, D> ArrayBase<S, D>
         sum
     }
 
+    /// Return a reference to a maximum of all values.
+    /// Return None if a comparison fails or if self is empty.
+    /// 
+    /// # Example
+    /// ```
+    /// use ndarray::arr2;
+    /// use std::f64;
+    /// 
+    /// let a = arr2(&[[1., 2.], [3., 4.]]);
+    /// 
+    /// assert_eq!(a.scalar_max(), Some(&4.));
+    /// 
+    /// let b = arr2(&[[1., f64::NAN], [3., 4.]]);
+    /// 
+    /// assert_eq!(b.scalar_max(), None);
+    /// ```
+    pub fn scalar_max(&self) -> Option<&A>
+    where A: PartialOrd
+    {
+        if let Some(slc) = self.as_slice_memory_order() {
+            let mut max = self.first();
+            for item in slc.iter().skip(1) {
+                match max.partial_cmp(&Some(item)) {
+                    None => return None,
+                    Some(::std::cmp::Ordering::Less) => max = Some(item),
+                    _ => {},
+                }
+            }
+            max
+        } else {
+            Zip::from(self).fold_while(self.first(), |acc, x| 
+            match acc.partial_cmp(&Some(x)) {
+                None => FoldWhile::Done(None),
+                Some(::std::cmp::Ordering::Less) => FoldWhile::Continue(Some(x)),
+                _ => FoldWhile::Continue(acc),
+            }).into_inner()
+        }
+    }  
+
+    /// Return a reference to a minimum of all values.
+    /// Return None if a comparison fails or if self is empty.
+    /// 
+    /// # Example
+    /// ```
+    /// use ndarray::arr2;
+    /// use std::f64;
+    /// 
+    /// let a = arr2(&[[1., 2.], [3., 4.]]);
+    /// 
+    /// assert_eq!(a.scalar_min(), Some(&1.));
+    /// 
+    /// let b = arr2(&[[1., f64::NAN], [3., 4.]]);
+    /// 
+    /// assert_eq!(b.scalar_min(), None);
+    /// ```
+    pub fn scalar_min(&self) -> Option<&A>
+    where A: PartialOrd
+    {
+        if let Some(slc) = self.as_slice_memory_order() {
+            let mut min = self.first();
+            for item in slc.iter().skip(1) {
+                match min.partial_cmp(&Some(item)) {
+                    None => return None,
+                    Some(::std::cmp::Ordering::Greater) => min = Some(item),
+                    _ => {},
+                }
+            }
+            min
+        } else {
+            Zip::from(self).fold_while(self.first(), |acc, x| 
+            match acc.partial_cmp(&Some(x)) {
+                None => FoldWhile::Done(None),
+                Some(::std::cmp::Ordering::Greater) => FoldWhile::Continue(Some(x)),
+                _ => FoldWhile::Continue(acc),
+            }).into_inner()
+        }
+    }  
+
     /// Return sum along `axis`.
     ///
     /// ```