eachindex is much slower than normal indexing for matrices

[abc]

For the following matrix

my_matrix = randn(10000, 1000)

using eachindex to access all elements is much slower than using ranges or even for el in my_matrix, even though it says in the documentation (http://docs.julialang.org/en/release-0.4/stdlib/arrays/#Base.eachindex) that eachindex uses ranges for Arrays.

Some code and numbers:

julia> sum = 0.0
julia> @time for iter in eachindex(my_matrix)
             sum += my_matrix[iter]
         end
   1.288944 seconds (50.00 M allocations: 915.519 MB, 3.36% gc time)

julia> sum = 0.0
julia> @time for i in 1:10000, j in 1:1000
             sum += my_matrix[i,j]
         end
   0.681678 seconds (34.38 M allocations: 524.582 MB, 2.45% gc time)

julia> sum = 0.0
julia> @time for el in my_matrix
             sum += el
         end
   1.063564 seconds (40.00 M allocations: 762.993 MB, 3.41% gc time)

Am I reading the documentation wrong, or is there something strange with the matrix indexing? Because as it is, I don't see any benefit of using anything different than simple ranges for manipulating matrices.

[Stefan Karpinski]

Can you try it not in global scope?

[abc]

Ah, yes, this seems to have fixed the problem, thank you.

Now, when not in global scope, using eachindex is definitely the fastest approach.
I made some measurements over 1000 runs for each of the approaches in the original post, here are the averages:
Using eachindex: 0.0026683
Using ranges: 0.0041256
Using in: 0.0031200

I guess I'll stick with eachindex. :)

[J Luis]

Incidentally, this errors in 0.5 (but works fine in 0.4)

julia> s=0.0;

julia> m=rand(10000,1000);

julia> @time for el in

m
              s = s + el
              end
ERROR: UndefVarError: s not defined
 [inlined code] from .\none:2
 in anonymous at .\no file:4294967295
 in eval at <invalid>:0

[Yichao Yu]

^^ I believe this one is also iterating in the wrong direction. Try
`for j in ..., for i in ...`

[Yichao Yu]

`for j in ... , i in ...` *

[J Luis]

Nope

julia> s=0.0;

julia> m=rand(10000,1000);

julia> @time for i in 1:10000, j in 1:1000

       s = s + m[i,j]

       end
ERROR: UndefVarError: s not defined
 [inlined code] from .\none:2
 in anonymous at .\no file:4294967295
 in eval at <invalid>:0

[Mauro]

On Thu, 2016-02-25 at 15:57, J Luis <jmf...@gmail.com> wrote:
> Incidentally, this errors in 0.5 (but works fine in 0.4)
>
> julia> s=0.0;
>
> julia> m=rand(10000,1000);
>
> julia> @time for el in m
> s = s + el
> end
> ERROR: UndefVarError: s not defined
> [inlined code] from .\none:2
> in anonymous at .\no file:4294967295
> in eval at <invalid>:0

I think this is https://github.com/JuliaLang/julia/issues/10472, or
might be related. I posted a minimal test case there.