Add function broadcast_with

src/impl_methods.rs

@@ -14,14 +14,14 @@ use rawpointer::PointerExt;
 
 use crate::imp_prelude::*;
 
-use crate::arraytraits;
+use crate::{arraytraits, BroadcastShape};
 use crate::dimension;
 use crate::dimension::IntoDimension;
 use crate::dimension::{
     abs_index, axes_of, do_slice, merge_axes, move_min_stride_axis_to_last,
     offset_from_ptr_to_memory, size_of_shape_checked, stride_offset, Axes,
 };
-use crate::error::{self, ErrorKind, ShapeError};
+use crate::error::{self, ErrorKind, ShapeError, from_kind};
 use crate::math_cell::MathCell;
 use crate::itertools::zip;
 use crate::zip::Zip;
@@ -1766,6 +1766,36 @@ where
         unsafe { Some(ArrayView::new(self.ptr, dim, broadcast_strides)) }
     }
 
+    /// Calculate the views of two ArrayBases after broadcasting each other, if possible.
+    ///
+    /// Return `ShapeError` if their shapes can not be broadcast together.
+    ///
+    /// ```
+    /// use ndarray::{arr1, arr2};
+    ///
+    /// let a = arr2(&[[2], [3], [4]]);
+    /// let b = arr1(&[5, 6, 7]);
+    /// let (a1, b1) = a.broadcast_with(&b).unwrap();
+    /// assert_eq!(a1, arr2(&[[2, 2, 2], [3, 3, 3], [4, 4, 4]]));
+    /// assert_eq!(b1, arr2(&[[5, 6, 7], [5, 6, 7], [5, 6, 7]]));
+    /// ```
+    pub fn broadcast_with<'a, 'b, B, S2, E>(&'a self, other: &'b ArrayBase<S2, E>) ->
+        Result<(ArrayView<'a, A, <D as BroadcastShape<E>>::Output>, ArrayView<'b, B, <D as BroadcastShape<E>>::Output>), ShapeError>
+    where
+        S: Data<Elem=A>,
+        S2: Data<Elem=B>,
+        D: Dimension + BroadcastShape<E>,
+        E: Dimension,
+    {
+        let shape = self.dim.broadcast_shape(&other.dim)?;
+        if let Some(view1) = self.broadcast(shape.clone()) {
+            if let Some(view2) = other.broadcast(shape) {
+                return Ok((view1, view2))
+            }
+        }
+        return Err(from_kind(ErrorKind::IncompatibleShape));
+    }
+
     /// Swap axes `ax` and `bx`.
     ///
     /// This does not move any data, it just adjusts the array’s dimensions

src/impl_ops.rs

@@ -106,9 +106,7 @@ where
             out.zip_mut_with_same_shape(rhs, clone_iopf(A::$mth));
             out
         } else {
-            let shape = self.dim.broadcast_shape(&rhs.dim).unwrap();
-            let lhs = self.broadcast(shape.clone()).unwrap();
-            let rhs = rhs.broadcast(shape).unwrap();
+            let (lhs, rhs) = self.broadcast_with(rhs).unwrap();
             Zip::from(&lhs).and(&rhs).map_collect_owned(clone_opf(A::$mth))
         }
     }
@@ -143,9 +141,7 @@ where
             out.zip_mut_with_same_shape(self, clone_iopf_rev(A::$mth));
             out
         } else {
-            let shape = rhs.dim.broadcast_shape(&self.dim).unwrap();
-            let lhs = self.broadcast(shape.clone()).unwrap();
-            let rhs = rhs.broadcast(shape).unwrap();
+            let (rhs, lhs) = rhs.broadcast_with(self).unwrap();
             Zip::from(&lhs).and(&rhs).map_collect_owned(clone_opf(A::$mth))
         }
     }
@@ -171,9 +167,7 @@ where
 {
     type Output = Array<A, <D as BroadcastShape<E>>::Output>;
     fn $mth(self, rhs: &'a ArrayBase<S2, E>) -> Self::Output {
-        let shape = self.dim.broadcast_shape(&rhs.dim).unwrap();
-        let lhs = self.broadcast(shape.clone()).unwrap();
-        let rhs = rhs.broadcast(shape).unwrap();
+        let (lhs, rhs) = self.broadcast_with(rhs).unwrap();
         Zip::from(&lhs).and(&rhs).map_collect(clone_opf(A::$mth))
     }
 }

tests/broadcast.rs

@@ -1,4 +1,5 @@
 use ndarray::prelude::*;
+use ndarray::{ShapeError, ErrorKind, arr3};
 
 #[test]
 #[cfg(feature = "std")]
@@ -81,3 +82,33 @@ fn test_broadcast_1d() {
     println!("b2=\n{:?}", b2);
     assert_eq!(b0, b2);
 }
+
+#[test]
+fn test_broadcast_with() {
+    let a = arr2(&[[1., 2.], [3., 4.]]);
+    let b = aview0(&1.);
+    let (a1, b1) = a.broadcast_with(&b).unwrap();
+    assert_eq!(a1, arr2(&[[1.0, 2.0], [3.0, 4.0]]));
+    assert_eq!(b1, arr2(&[[1.0, 1.0], [1.0, 1.0]]));
+
+    let a = arr2(&[[2], [3], [4]]);
+    let b = arr1(&[5, 6, 7]);
+    let (a1, b1) = a.broadcast_with(&b).unwrap();
+    assert_eq!(a1, arr2(&[[2, 2, 2], [3, 3, 3], [4, 4, 4]]));
+    assert_eq!(b1, arr2(&[[5, 6, 7], [5, 6, 7], [5, 6, 7]]));
+
+    // Negative strides and non-contiguous memory
+    let s = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
+    let s = Array3::from_shape_vec((2, 3, 2).strides((1, 4, 2)), s.to_vec()).unwrap();
+    let a = s.slice(s![..;-1,..;2,..]);
+    let b = s.slice(s![..2, -1, ..]);
+    let (a1, b1) = a.broadcast_with(&b).unwrap();
+    assert_eq!(a1, arr3(&[[[2, 4], [10, 12]], [[1, 3], [9, 11]]]));
+    assert_eq!(b1, arr3(&[[[9, 11], [10, 12]], [[9, 11], [10, 12]]]));
+
+    // ShapeError
+    let a = arr2(&[[2, 2], [3, 3], [4, 4]]);
+    let b = arr1(&[5, 6, 7]);
+    let e = a.broadcast_with(&b);
+    assert_eq!(e, Err(ShapeError::from_kind(ErrorKind::IncompatibleShape)));
+}