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Support zero-length axis in .map_axis/_mut() #579
Description
The implementation of .map_axis/_mut() panics when the specified axis is zero-length. Ideally, we'd just apply mapping to empty views instead.
Example:
extern crate ndarray;
use ndarray::prelude::*;
fn main() {
let a = Array2::<f32>::zeros((0, 2));
a.map_axis(Axis(0), |_| {});
}
Activity
andrei-papou commentedon Mar 25, 2019
Hi @jturner314 . I can work on this one if you don't mind.
jturner314 commentedon Mar 25, 2019
@andrei-papou Sure, please feel free.
andrei-papou commentedon Mar 27, 2019
@jturner314 could you please point me to an example of creating an empty array? Thanks a lot.
jturner314 commentedon Mar 27, 2019
The simplest way to create a 1-dimensional, zero-length view in
map_axiswould beunsafe { ArrayView::new_(std::ptr::NonNull::<A>::dangling().as_ptr(), Ix1(0), Ix1(0)) }. See this commentary.Edit: If that doesn't compile, you might need a cast:
unsafe { ArrayView::new_(std::ptr::NonNull::<A>::dangling().as_ptr() as *const A, Ix1(0), Ix1(0)) }.andrei-papou commentedon Mar 29, 2019
@jturner314 thanks. please take a look at the PR #612
jturner314 commentedon Apr 2, 2019
Fwiw, I realized that a cleaner (safe) way to create a zero-length one-dimensional view is
ArrayView1::from(&[]).jblondin commentedon Apr 19, 2019
PR was merged. Is anything still remaining here, or can this issue be closed?
jturner314 commentedon Apr 19, 2019
Fixed by #612. Thanks for following up.