FEAT: Add method .shift_remove_index

Author: bluss

src/impl_methods.rs

@@ -2444,6 +2444,35 @@ where
         }
     }
 
+    /// Remove each `index`th element along `axis` and shift down elements from higher indexes.
+    ///
+    /// Decreases the length of `axis` by one.
+    ///
+    /// ***Panics** if `axis` or `index` is out of bounds.
+    pub fn shift_remove_index(&mut self, axis: Axis, index: usize)
+    where
+        S: DataOwned + DataMut,
+    {
+        // TODO: It's possible to choose to shift the elment to the front or the back here,
+        // whichever is closer.
+        let (_, mut tail) = self.view_mut().split_at(axis, index);
+        // shift elements to the back
+        // use swap to keep all elements initialized (as required by owned storage)
+        if tail.len_of(axis) > 1 {
+            Zip::from(tail.lanes_mut(axis)).for_each(|lane| {
+                // TODO give ArrayViewMut1 a split_first method?
+                let (mut fst, mut rest) = lane.split_at(Axis(0), 1);
+                let mut dst = &mut fst[0];
+                for elt in rest.iter_mut() {
+                    std::mem::swap(dst, elt);
+                    dst = elt;
+                }
+            });
+        }
+        // then slice the axis in place to cut out the removed final element
+        self.slice_axis_inplace(axis, Slice::new(0, Some(-1), 1));
+    }
+
     /// Iterates over pairs of consecutive elements along the axis.
     ///
     /// The first argument to the closure is an element, and the second

tests/array.rs

@@ -2397,3 +2397,45 @@ mod array_cow_tests {
         });
     }
 }
+
+#[test]
+fn test_shift_remove() {
+    let mut a = arr2(&[[1, 2, 3],
+                       [4, 5, 6],
+                       [7, 8, 9],
+                       [10,11,12]]);
+    a.shift_remove_index(Axis(0), 1);
+    a.shift_remove_index(Axis(1), 2);
+    assert_eq!(a.shape(), &[3, 2]);
+    assert_eq!(a,
+        array![[1, 2],
+               [7, 8],
+               [10,11]]);
+
+    let mut a = arr2(&[[1, 2, 3],
+                       [4, 5, 6],
+                       [7, 8, 9],
+                       [10,11,12]]);
+    a.invert_axis(Axis(0));
+    a.shift_remove_index(Axis(0), 1);
+    a.shift_remove_index(Axis(1), 2);
+    assert_eq!(a.shape(), &[3, 2]);
+    assert_eq!(a,
+        array![[10,11],
+               [4, 5],
+               [1, 2]]);
+
+    a.shift_remove_index(Axis(1), 1);
+
+    assert_eq!(a.shape(), &[3, 1]);
+    assert_eq!(a,
+        array![[10],
+               [4],
+               [1]]);
+    a.shift_remove_index(Axis(1), 0);
+    assert_eq!(a.shape(), &[3, 0]);
+    assert_eq!(a,
+        array![[],
+               [],
+               []]);
+}