# [Numpy-discussion] array - dimension size of 1-D and 2-D examples

Vinodhini Balusamy me.vinob at gmail.com
Mon Jan 8 06:20:15 EST 2018

Missed this mail.
Thanks Derek For the clarification provided.

Kind Rgds,
Vinodhini

> On 31 Dec 2017, at 10:11 am, Derek Homeier <derek at astro.physik.uni-goettingen.de> wrote:
>
> On 30 Dec 2017, at 5:38 pm, Vinodhini Balusamy <me.vinob at gmail.com> wrote:
>>
>> Just one more question from the details you have provided which from my understanding strongly seems to be Design
>> [DEREK] You cannot create a regular 2-dimensional integer array from one row of length 3
>>> and a second one of length 0. Thus np.array chooses the next most basic type of
>>> array it can fit your input data in
>>
> Indeed, the general philosophy is to preserve the structure and type of your input data
> as far as possible, i.e. a list is turned into a 1d-array, a list of lists (or tuples etc…) into
> a 2d-array,_ if_ the sequences are of equal length (even if length 1).
> As long as there is an unambiguous way to convert the data into an array (see below).
>
>>   Which is the case,  only if an second one of length 0 is given.
>>   What about the case 1 :
>>>>> x12 = np.array([[1,2,3]])
>>>>> x12
>> array([[1, 2, 3]])
>>>>> print(x12)
>> [[1 2 3]]
>>>>> x12.ndim
>> 2
>>>>>
>>>>>
>> This seems to take 2 dimension.
>
> Yes, structurally this is equivalent to your second example
>
>> also,
>>>> x12 = np.array([[1,2,3],[0,0,0]])
>>>> print(x12)
> [[1 2 3]
> [0 0 0]]
>>>> x12.ndim
> 2
>
>> I presumed the above case and the case where length 0 is provided to be treated same(I mean same behaviour).
>> Correct me if I am wrong.
>>
> In this case there is no unambiguous way to construct the array - you would need a shape (2, 3)
> array to store the two lists with 3 elements in the first list. Obviously x12[0] would be np.array([1,2,3]),
> but what should be the value of x12[1], if the second list is empty - it could be zeros, or repeating x12[0],
> or simply undefined. np.array([1, 2, 3], [4]]) would be even less clearly defined.
> These cases where there is no obvious “right” way to create the array have usually been discussed at
> some length, but I don’t know if this is fully documented in some place. For the essentials, see
>
> https://docs.scipy.org/doc/numpy/reference/routines.array-creation.html
>
> note also the upcasting rules if you have e.g. a mix of integers and reals or complex numbers,
> and also how to control shape or data type explicitly with the respective keywords.
>
> 					Derek
>
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