Add an example for an equivalent of numpy's column_stack function in ndarray_for_numpy_users

[synasius]

I was looking for an equivalent function of numpy's column_stack (see https://docs.scipy.org/doc/numpy/reference/generated/numpy.column_stack.html) in ndarray docs.

This is how I managed to solve the issue:

use ndarray::{Array, Axis, stack, arr2};

let a = Array::linspace(0., 1., 5).into_shape((5,1)).unwrap();
let b = Array::<f64, _>::ones((5, 1));
let res = stack(Axis(1), &[b.view(), a.view()]);
assert!(res == Ok(arr2(&[[1., 0.],
                 [1., 0.25],
                 [1., 0.5],
                 [1., 0.75],
                 [1., 1.]])));

It could be worth to have an example in ndarray_for_numpy_users section of the docs.

[AndreasH96]

Is this issue still active? I'm interested in starting contributing and this seems like a good start 😄