[Numpy-discussion] Added atleast_nd, request for clarification/cleanup of atleast_3d

[Juan Nunez-Iglesias]

We use np.at_least2d extensively in scikit-image, and I also use it in a
*lot* of my own code now that scikit-learn stopped accepting 1D arrays as
feature vectors.

> what is the advantage of np.at_leastnd` over `np.array(a, copy=False,
ndim=n)`

Readability, clearly.

My only concern is the described behavior of np.at_least3d, which came as a
surprise. I certainly would expect the “at_least” family to all work in the
same way as broadcasting, ie prepending singleton dimensions.
Prepend/append behavior can be controlled either by keyword or simply by
using .T, I don’t mind either way.

Juan.

On 6 July 2016 at 10:22:15 AM, Marten van Kerkwijk (
m.h.vankerkwijk at gmail.com) wrote:

Hi All,

I'm with Nathaniel here, in that I don't really see the point of these
routines in the first place: broadcasting takes care of many of the initial
use cases one might think of, and others are generally not all that well
served by them: the examples from scipy to me do not really support
`at_least?d`, but rather suggest that little thought has been put into
higher-dimensional objects which should be treated as stacks of row or
column vectors. My sense is that we're better off developing the direction
started with `matmul`, perhaps adding `matvecmul` etc.

More to the point of the initial inquiry: what is the advantage of having a
general `np.at_leastnd` routine over doing
```
np.array(a, copy=False, ndim=n)
```
or, for a list of inputs,
```
[np.array(a, copy=False, ndim=n) for a in input_list]
```

All the best,

Marten
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