# Setting number of threads and parsing arguments
**URL:** https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904
**Category:** New to Julia
**Tags:** first-steps, shell, repl, multithreading, excel
**Created:** [March 25, 2021, 2:04am UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904 "2021-03-25T02:04:07Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@mjanun](https://discourse.julialang.org/u/mjanun)
#### Post date: [March 25, 2021, 2:04am UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904/1 "2021-03-25T02:04:07Z")
I understand that to launch Julia with multithreading from command prompt (on Windows), one has to pass the following command before launching Julia: `set JULIA_NUM_THREADS=4`
I am calling Julia from Excel/VBA using the Shell command. Calling Julia from VBA is simple but I am not sure how to launch it with a specific number of threads and then to execute some Julia code.
A simple example can be something like this:
```julia
# VBA code
Sub run()
code = "C:\Documents\Julia\read.jl"
file_1 = "C:/Documents/Julia/file1_data.csv"
file_2 = "C:/Documents/Julia/file2_data.csv"
file_3 = "C:/Documents/Julia/file3_data.csv"
var1 = 3.1
var2 = 2.2
Call Shell("cmd /S /K" & "julia" & " " & code & " " & file_1 & & " " & file_2 & " " & file_3 & " " var1 & " " & var2)
End
```
```julia
# file name: read.jl
function read(file1,file2,file3, var1,var2)
println("File 1 is ",file1)
println("File 2 is ",file2)
println("File 3 is ",file£)
println("Variable 1 is ",var1)
print("Variable 2 is ",var2)
end
file1 = ARGS[1]
file2 = ARGS[2]
file3 = ARGS[3]
var1 = parse(Float64,ARGS[4])
var2 = parse(Float64,ARGS[5])
read(file1,file2,file3, var1,var2)
```
May I ask, how to pass the command set JULIA\_NUM\_THREADS=4 to the above VBA code?
In Julia code, I have about 20 files that are being read (only 3 are shown in the MWE). Do I have to type for each argument …= ARGS[i] for file names and …= parse(Float64,ARGS[i]) for any numerical values (as shown above)? Can this be done using a custom struct or a vector instead? If so, an example of this will be much appreciated.
---
### Author:  [@stillyslalom](https://discourse.julialang.org/u/stillyslalom)
#### Post date: [March 25, 2021, 2:32am UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904/2 "2021-03-25T02:32:34Z")
For recent versions of Julia, you can use the `-t` flag to specify the number of threads at launch (e.g. `julia -t 4`).
You can ‘slurp’ and ‘splat’ arguments with `...`:
```julia
files = [ARGS[1:20]...]
vars = parse.(Int, ARGS[21:end])
read(files..., vars...)
```
The docs provide more details:
```julia
help?> ...
search: ...
...
The "splat" operator, ..., represents a sequence of arguments. ... can be used in
function definitions, to indicate that the function accepts an arbitrary number of
arguments. ... can also be used to apply a function to a sequence of arguments.
Examples
≡≡≡≡≡≡≡≡≡≡
julia> add(xs...) = reduce(+, xs)
add (generic function with 1 method)
julia> add(1, 2, 3, 4, 5)
15
julia> add([1, 2, 3]...)
6
julia> add(7, 1:100..., 1000:1100...)
111107
```
---
### Author:  [@mjanun](https://discourse.julialang.org/u/mjanun)
#### Post date: [March 25, 2021, 4:59pm UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904/3 "2021-03-25T16:59:27Z")
Thank you.
> [@stillyslalom](#):
>
> You can ‘slurp’ and ‘splat’ arguments with `...` :
>
> ```julia
>
> ```
I need a bit more help here. As I understand, splat arguments are used when the function accepts an arbitrary number of arguments. My function accepts a fixed number of arguments but there are too many arguments.
Is it not better to use `struct` to define input arguments in that case? Are there any example that explains use of struct instead of using too many variables to define inputs (as in the MWE)?
---
### Author:  [@stillyslalom](https://discourse.julialang.org/u/stillyslalom)
#### Post date: [March 25, 2021, 5:11pm UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904/4 "2021-03-25T17:11:10Z")
Packing things into a `struct` can allow the compiler to perform certain optimizations that are unavailable for `Array`, but that shouldn’t be too important for a case like this (since your struct elements would include strings, which aren’t `isbits` and thus can’t be stored inline). A struct is also useful if you want to specialize the behavior or provide custom getters/setters, but it’s not clear to me that your application calls for that. The right choice will depend on what’s happening within `read` - could you expand on that?
---
### Author:  [@mjanun](https://discourse.julialang.org/u/mjanun)
#### Post date: [March 25, 2021, 5:40pm UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904/5 "2021-03-25T17:40:31Z")
`read` is reading CSV files and passing the data in format of dataframes to other functions for processing. These csv files contains both numerical data and strings. Other functions are doing numerical computations and data manipulation using DataFrames package. I am not sure if this give you enough to advice.
> [@stillyslalom](#):
>
> A struct is also useful if you want to specialize the behavior or provide custom getters/setters, but it’s not clear to me that your application calls for that.
I do want to specialise the behaviour depending upon the input arguments, e.g., say one of the input arguments `var1` accepts either a vector of two dimensions type Float64 or a single Float64 number and then dispatches the right function. I think it requires defining a parametric type but I am still trying to learn how to use it in practice.
---
### Author:  [@stillyslalom](https://discourse.julialang.org/u/stillyslalom)
#### Post date: [March 25, 2021, 6:11pm UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904/6 "2021-03-25T18:11:20Z")
It doesn’t necessarily require a parametric type - you can provide runtime dispatch with something like
```julia
...
process_var1(var1::Array{Float64, 2}) = ...
process_var1(var1::Float64) = ...
...
function read(files, vars)
dfs = [DataFrame(CSV.File(file)) for file in files]
...
result1 = process_var1(vars[1])
...
end
```
---
### Author:  [@mjanun](https://discourse.julialang.org/u/mjanun)
#### Post date: [March 25, 2021, 6:36pm UTC](https://discourse.julialang.org/t/setting-number-of-threads-and-parsing-arguments/57904/7 "2021-03-25T18:36:34Z")
Thank you