# Calling a package function with a parallelized for loop

**URL:** <https://discourse.julialang.org/t/calling-a-package-function-with-a-parallelized-for-loop/24986>\
**Category:** New to Julia\
**Created:** [June 5, 2019, 10:16pm UTC](https://discourse.julialang.org/t/calling-a-package-function-with-a-parallelized-for-loop/24986 "2019-06-05T22:16:49Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![bigoten](https://avatars.discourse-cdn.com/v4/letter/b/f0a364/32.png) [@bigoten](https://discourse.julialang.org/u/bigoten)\
**Post date:** [June 5, 2019, 10:16pm UTC](https://discourse.julialang.org/t/calling-a-package-function-with-a-parallelized-for-loop/24986/1 "2019-06-05T22:16:49Z")

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I want to run some code in parallel, however I found a strange behavior that I would like to understand.  
Here is a small working example:

```julia
using Random;
using Statistics;
using Distributed;
using SharedArrays;

nprocs()
addprocs(3);

nreps = 5;
result = SharedArray{Float64, 1}(nreps);
@distributed for i = 1:nreps
    data = randn(20);
    result[i] = Statistics.mean(data);
end;

```

This silly code simply computes the mean of a random sample from N(0, 1) of size 20, nreps times.  
What bothers me is that the code breaks in case the second last line is simply the following:

```julia
    result[i] = mean(data);

```

Now, array ‘result’ was never changed in the for loop (it’s still full of 0s). Why is this? How can I simply call a function by its name, without explicitly referring to its package? And why isn’t function ‘randn’ suffering from the same problem?

This is a problem to me because the for loop that I really want to implement has many calls to a variety of functions (e.g., var, sd, tdistcdf), and keeping track of the package of each function seems a waste of typing effort and space. I do understand this behavior when there are multiple packages offering a function with the same name (this also happens to me a lot in R, which is my main programming language), but that is definitely not the explanation here.

Many thanks in advance,  
bigoten

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**Author:** ![jpsamaroo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jpsamaroo/32/46804_2.png) [@jpsamaroo](https://discourse.julialang.org/u/jpsamaroo)\
**Post date:** [June 5, 2019, 10:53pm UTC](https://discourse.julialang.org/t/calling-a-package-function-with-a-parallelized-for-loop/24986/2 "2019-06-05T22:53:50Z")

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The first problem is the load order puts `using Statistics` before `addprocs(3)`. Those `using` statements at the top of your script will **not** be evaluated on new workers, so you should do `using Statistics` after `addprocs(3)`.

The second problem is that even after a `using` on the master when workers are present, the package is not loaded into `Main` on the workers like it is on the master; so you need to specify the module explicitly. You can fix this by executing `@everywhere using Statistics` to export the contents of `Statistics` into `Main`.

The third problem, which is not really your fault, is that apparently `@distributed` doesn’t print worker errors (such as `mean` not being defined in `Main`) to the master; there very well could be an issue for this on the Julia Github tracker, but I haven’t managed to locate one that matches yet.

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**Author:** ![bigoten](https://avatars.discourse-cdn.com/v4/letter/b/f0a364/32.png) [@bigoten](https://discourse.julialang.org/u/bigoten)\
**Post date:** [June 6, 2019, 8:17pm UTC](https://discourse.julialang.org/t/calling-a-package-function-with-a-parallelized-for-loop/24986/3 "2019-06-06T20:17:39Z")

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Thank you @jpsamaroo! My code is finally running due to your explanation, plus I understood better what is happening. Thanks a lot 👍