[Python-ideas] Python multi-dimensional array constructor

[Chris Barker]

a few thoughts:

On Wed, Oct 19, 2016 at 12:08 PM, Todd <toddrjen at gmail.com> wrote:

> I have been thinking about how to go about having a multidimensional array
> constructor in python.  I know that Python doesn't have a built-in
> multidimensional array class and won't for the foreseeable future.
>

no but it does have buffers and memoryviews and the extended buffer
protocol supports "strided" data -- i.e. multi-dimensional arrays. So it
would be nice to have SOME simple ndarray object in the standard library
that would wrap such buffers -- it would be nice for working with image
data, interacting with numpy  arrays, etc.

The "trick" is that once you have the container, you want some
functionality -- so you add indexing and slicing -- natch. Then maybe some
simple math? then.... eventually, you are trying to put all of numpy into
the stdlib, and we already know we don't want to do that.

Though I still think a simple container that only supports indexing and
slicing would be lovely.

That all being said:

a = [| 0, 1, 2 || 3, 4, 5 |]
>

I really don't see the advantage of that over:

a = [[0, 1, 2],[3, 4, 5]]

really I don't -- and I'm a heavy numpy user, so I write a lot of those!

If there is a problem with the current options (and I'm not convinced there
is) it's that it in'st a literal for multidimensional array, but rather a
literal for a bunch of nested lists -- the list themselves are created, and
so are all the "boxed" values in the array -- only to be pulled out and
unboxed to be put in the array.

However, this is only for literals -- if your data are large, then they are
not going to be in literals, but rather read form a file or something, so
this is really not much of a limitation.

However, if you really don't like it, then you can pass a string to
aconfsturctor function instead:

a = arr_from_string(" | 0, 1, 2 || 3, 4, 5 | ")

yeah, you need to type the extra quotes, but that's not much.

NOTE: I'm pretty sure numpy has something like this already, for folks that
like the MATLAB style -- though I can't find it at the moment.

b = [| 0, 1, 2 |
>      | 3, 4, 5 |]
>

b = [[ 0, 1, 2 ],
     [ 3, 4, 5 ]]


You can also create a 2D row array by combining the two:
>
> a = [|| 0, 1, 2 ||]
>

a = [[ 0, 1, 2 ]] or is it: [[[ 0, 1, 2 ]]]

(I can't tell, so maybe your syntax is not so clear???



> For higher dimensions, you can just put more lines together:
>
> a = [||| 0, 1, 2 || 3, 4, 5 ||| 6, 7, 8 || 9, 10, 11 |||]
>
> b = [||| 0, 1, 2
>       || 3, 4, 5
>      ||| 6, 7, 8
>       || 9, 10, 11
>      |||]
>

I have no idea what that means!


> c = [||| 0, 1, 2 |
>        | 3, 4, 5 |
>      |
>        | 6, 7, 8 |
>        | 9, 10, 11 |||]
>
>
> A 3D row vector would just be:
>
> a = [||| 0, 1, 2 |||]
>
> A 3d column vector would be:
>
> a = [||| 0 || 1 || 2 |||]
>



> b = [||| 0
>       || 1
>       || 2
>      |||]
>
> A 3D depth vector would be:
>
> a = [||| 0 ||| 1 ||| 2 |||]
>
> b = [||| 0
>      ||| 1
>      ||| 2
>      |||]
>

nor these....



> At least in my opinion, this sort of approach really shines when making
> higher-dimensional arrays.  These would all be equivalent (the | at the
> beginning and end are just to make it easier to align indentation, they
> aren't required):
>
> a = [|||| 48, 11, 141, 13, -60, -37, 58, -52, -29, 134
>        || -6, 96, -66, 137, -59, -147, -118, -104, -123, -7
>       ||| -103, 50, -89, -12,  28, -12, 119, -131, -73, 21
>        || -58, 105, 25, -138, -106, -118, -29, -49, -63, -56
>      |||| -43, -34, 101, -115, 41, 121, 3, -117, 101, -145
>        || 100, -128, 76, 128, -113, -90, 52, -91, -72, -15
>       ||| 22, -65, -118, 134, -58, 55, -73, -118, -53, -60
>        || -85, -136, 83, -66, -35, -117, -71, 115, -56, 133
>      ||||]
>

it does seem that you are saving some typing when you have high-dim arrays,
but I really dont see the readability here.

>
> I think both of the new examples are considerably clearer than the current
> approach.
>

not to me :-(


but anyway, the way to more this kind of thing forward is to use it as a
new format in an existing lib (like numpy, by passing it as a big string.
IF folks like it and start using it, then there is room for a conversation.

But I doubt (and I wouldn't support) that anyone would put a literal into
python for an object that doesn't exist in python...

-CHB


-- 

Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
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Chris.Barker at noaa.gov
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