Document NdProducer::raw_dim

[jturner314]

This is useful because, otherwise, users have to manually calculate the shape of the producer to e.g. allocate an array of the correct shape to zip with it.

[bluss]

Users can use .map_collect to have an array of the right shape and layout. I'm also drafting something that makes it easy to do something like this: Array::zeros(a.shape_builder()) to get an array of the same shape and layout (coarsely defined - probably only selecting C/F).

[jturner314]

Users can use .map_collect to have an array of the right shape and layout.

Right; my earlier comment wasn't clear. I'm thinking specifically of a discussion with a user on #rust-sci who wanted to copy windows of an ArrayView1 into columns of a new Array2. Calling Zip::from(arr_1d.windows()).map_collect(...) would result in Array1<...>. If NdProducer::raw_dim is exposed, then the following works:

fn windows_to_cols<A>(arr: ArrayView1<'_, A>, window_len: usize) -> Array2<A>
where
    A: Clone + Zero,
{
    let windows = arr.windows(window_len);
    let mut out = Array2::zeros([window_len, windows.raw_dim()[0]].f());
    azip!(
        (mut col in out.axis_iter_mut(Axis(1)), window in windows)
        col.assign(&window)
    );
    out
}

I'm also drafting something that makes it easy to do something like this: Array::zeros(a.shape_builder()) to get an array of the same shape and layout (coarsely defined - probably only selecting C/F).

That would be convenient.