Thanks for the additional clarification David.
On Saturday, July 25, 2015 at 12:00:24 PM UTC-4, David Gold wrote:
>
> To supplement John's resource (which explains that the behavior you
> indicate is indeed a property of the language):
>
> Currently (and in the version you're using), range indexing such as `x[:]`
> returns a copy of `x`. So does applying an operation like `y * 4`. That's
> why writing `y = x[:]` or `y = y * 4` doesn't reassign `y` in such a way
> that subsequent modifications to `y` impact `x`.
>
> On Saturday, July 25, 2015 at 11:13:33 AM UTC-4, Christopher Fisher wrote:
>>
>> I am writing a program (in .3.1) that takes a one dimensional array of
>> indices (x) and creates a new one dimensional array of indices (x = y) and
>> switches a given pair of elements in the new array. For some reason, the
>> original array (x) changes when I change the new array (see below).
>>
>> In [16]:
>>
>> x = [1:5]
>>
>> y = x
>>
>> y[[3;4]] = y[[4;3]]
>>
>> [x y]
>>
>> Out[16]:
>>
>> 5x2 Array{Int64,2}:
>> 1 1
>> 2 2
>> 4 4
>> 3 3
>>
>>
>>
>> However, if I change y = x to y = x[:], the problem does not occur, even
>> though x and x[:] appear to be the same type.
>>
>>
>> In [15]:
>>
>> x = [1:5]
>>
>> y = x[:]
>>
>> y[[3;4]] = y[[4;3]]
>>
>> [x y]
>>
>> Out[15]:
>>
>> 5x2 Array{Int64,2}:
>> 1 1
>> 2 2
>> 3 4
>> 4 3
>> 5 5
>>
>>
>> The code below shows that this does not seem to be a general property of the
>> language. As in the previous cases, I define y as x and change y.
>>
>>
>> In [13]:
>>
>> x = [1:5]
>>
>> y = x
>>
>> y = y*4
>>
>> [x y]
>>
>> Out[13]:
>>
>> 5x2 Array{Int64,2}:
>> 1 4
>> 2 8
>> 3 12
>> 4 16
>> 5 20
>>
>>
>>
>> Certainly, I could use y = x[:] or simply change the original array.
>> Nonetheless, the inconsistency seems undesirable from my point of view. Is
>> this a bug? Any help would be appreciated.
>>
>>
>>
