>
> As you can see, `ArrayComprehension` is more likely to be a such
> structure: [[[...]...]...].
Ahh...I see what you mean about the multidimensionality, now. It is a *reshaped
*list comprehension:
>>> reshape([i + j for i in range(4) for j in range(3) for k in
range(2)], [[2]]*3)
[[[0, 0], [1, 1], [2, 2]], [[1, 1], [2, 2], [3, 3]], [[2, 2], [3, 3],
[4, 4]], [[3, 3], [4, 4], [5, 5]]]
>>> _==S(str(ArrayComprehension(i+j ,(i,0,3),(j,0,2),(k,0,1)).doit()))
True
So I see the reason not to call it a List.
On Tuesday, June 4, 2019 at 4:23:20 AM UTC-5, Zhiqi KANG wrote:
>
> Hi,
>
> As far as I know, the difference between `ArrayComprehension` and `list`
> lies in the notion of multidimensionality.
>
> First of all, for clarification,
>
> > `List(i + j, (i,0,3), (j,0,4))` is the unevaluated form of `[i + j for i
> in range(4) for j in range(5)]`.
>
> is not quite true regarding the implementation of `ArrayComprehension`. In
> fact, `ArrayComprehension(i + j, (i,0,3), (j,0,4))` will be like `[[i + j
> for i in range(5)] for j in range(4)]`. Not to mention the different order
> of dimensions because the limits in `ArrayComprehension` are executed from
> left to right, the resulting output is a multidimensional list. So each
> time there is one more limit, the dimension of output list will +1. As you
> can see, `ArrayComprehension` is more likely to be a such structure:
> [[[...]...]...]. This multidimensionality comes from Table
> <https://reference.wolfram.com/language/ref/Table.html> in Wolfram
> Mathematica, which is the the example of the implementation of
> `ArrayComprehension`.
>
> Secondly, the implementation follows the example of `Array` module in
> SymPy, which means the properties and functions like `shape`, `rank()` have
> been already implemented.Plus, its output is of type
> `ImmutableDenseNDimArray`. Since an array has by default a notion of
> multidimensionality, it would be more coherent to call it as an array.
> That's why its name is `ArrayComprehension` rather than
> `ListComprehension`.
>
> However, it is no doubt that `ArrayComprehension` resembles a lot to list.
> It would be a good idea to have something similar to list implemented in
> SymPy, in order to add a notion of 'immutable' to list. Either renaming
> ArrayComprehension or creating a new module to do so is faisible.
>
> That's what I have understood while implementing `ArrayComprehension`. I
> hope that it could help make some concepts clear.
>
> Zhiqi
>
>
> 在 2019年6月4日星期二 UTC+2上午5:46:03，Chris Smith写道：
>>
>> From discussion at #16926 <https://github.com/sympy/sympy/pull/16929> where
>> I suggest that perhaps we should be naming ArrayComprehension as List and
>> it was said,
>>
>> > [ArrayComprehension] is supposed to be a multidimensional list
>> comprehension
>>
>> It looks like an unevaluated List to me: `List(i + j, (i,0,3), (j,0,4))`
>> is the unevaluated form of `[i + j for i in range(4) for j in range(5)]`.
>> (For comparison, Integral and Sum are examples of an unevaluated Expr,
>> which, after a doit and the right conditions, lose the wrapper and become
>> other Expr.)
>>
>> An evaluated form would be `List([1, 2, 3, 4])` where the `[]` would be
>> necessary to distinguish between the evaluated and comprehension form.
>>
>> Are we going to regret introducing an object that is so closely related
>> to a list or will we always want a list to be an unsympified object in
>> SymPy?
>>
>> /c
>>
>
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