reshape question

[Gabor]

I would like to view the same data sometimes as 1D and sometimes as 2D.

 

A simple test case is this:

 

> a = reshape(1:4,2,2)
> b = reshape(a,4)
> a[1] = 99

> a
2x2 Int32 Array:
 99  3
  2  4

> b
4-element Int32 Array:
 99
  2
  3
  4

Fine, it works as expected.
Let's try this the other way around:

> a = reshape(1:4,4)
> b = reshape(a,2,2)
> a[1] = 99

> a
2x2 Int32 Array:
 99  3
  2  4

> b
4-element Int32 Array:
 99
  2
  3
  4

It works again.
Now, let's get rid of the first reshape:

> a = [1:4]
> b = reshape(a,2,2)
> a[1] = 99

> a
4-element Int32 Array:
 99
  2
  3
  4

> b
2x2 Int32 Array:
 1  3
 2  4

 

 

Bummer, it does not work as I expected.

 

Could someone please explain why?

[Viral Shah]

See this discussion: https://github.com/JuliaLang/julia/issues/2279

Also, in this case, you would be better off with just creating a 2D array, and indexing it with either 1 or 2 indices. All arrays can be accessed with linear indexing. You do not need to use reshape here:

julia> a = [1 2; 3 4]

2x2 Int64 Array:

 1  2

 3  4

julia> a[1]

1

julia> a[3]

2

julia> a[2,2]

4

[Gabor]

 

Thank you for the explanation and the pointer, Viral!

In the meantime I realized that my third example also works,

this behaviour was changed at the version 0.1.2  (March 8)

and I was still using the version 0.1.0 (February 19).