[R] R equivalent of python module structure and functionality?

[Tom Roche]

https://stat.ethz.ch/pipermail/r-help/2012-September/323551.html (slightly edited)
>> how to structure an R file such that it can be both

>> 1. used as a script via, e.g., (from OS commandline)

>> $ Rscript foo.r bar=baz

>> 2. imported and called as a function via, e.g. (from R commandline)

>> > source('./foo.r')

>> or otherwise loaded, then called, e.g.

>> > foo(bar='baz')

>> ? I'm looking for the 'R equivalent' of how python supports this

Big thanks to Trevor Davis!

https://stat.ethz.ch/pipermail/r-help/2012-September/323559.html
> The optparse package is what you would want [to parse args for] a
> script i.e.``Rscript foo.R --bar=baz`` in a pythonic manner.

Unfortunately, the R on the cluster on which I'm working currently
lacks that package, and I lack root on that cluster. But your example
(below) works on my box (where I'm root).

> The other piece of the puzzle is the ``interactive()`` function
> which lets you know if you are are calling from the "R commandline".
...
> Example:

one syntax error fixed
> ### begin foo.R #####

> # define foo function
> foo <- function(bar) {
>    print(bar)
> }

> # if not interactive we are calling from OS command line
> # parse args and call function foo
> if(!interactive()) {
>    suppressPackageStartupMessages(library("optparse"))
>   option_list <- list(
>      make_option(c("-b", "--bar"), default="hello world")
>   )
>   opt <- parse_args(OptionParser(option_list=option_list))
>   foo(bar=opt$bar)
> }

> ##### end foo.R  ######

And I have modified my code @

https://github.com/TomRoche/GEIA_to_netCDF/commit/f982de0660b10f380183e34a0f1557a4cb1c5bb7

accordingly (to use `interactive()`, anyway).

Thanks again! Tom Roche <Tom_Roche at pobox.com>