[R] Making objects global in a package

[Jeff Newmiller]

a) There is a mailing list for package development questions: R-package-devel.

b) This seems like a job for the sysdata.rda file... no explicit environments needed. See the Writing R Extensions manual.

On July 13, 2018 5:51:06 PM PDT, Michael Hannon <jmhannon.ucdavis using gmail.com> wrote:
>Greetings.  I'm putting together a small package in which I use
>`dplyr::read_csv()` to read CSV files from several different sources. 
>I do
>this in several different files, but with various kinds of subsequent
>processing, depending on the file.
>
>I find it useful to specify column types, as the apparent data type of
>a given
>column sometimes changes unexpectedly deep into the file.  I.e., a
>field that
>consistently looks like an integer, suddenly becomes a fraction:
>
>    1, 1, ..., 1, 1/2, 1, ...
>
>Hence, the column type has to be treated as a character, rather than as
>an
>integer (with the possibility of later conversion to double, if
>necessary).
>(This is just an example.)
>
>Therefore I use the `col_types` argument in all of the calls to
>`read_csv()`.
>
>These calls are spread over several files, but I want the keep all of
>the
>column types in a single place, yet have them available in each of the
>several
>files.  This is just for the sake of maintainability.
>
>At the moment I do this by putting the column-type definitions into a
>single,
>file:
>
>    000_define_data_attributes.R
>
>that:
>
>    (1) is named so that it's parsed first by `devtools::build()`
>    (2) sets up an environment and stuffs the column types into it:
>
>            data_env <- new.env(parent=emptyenv())
>            data_env$col_types_alpha <- list(
>                Date = col_date(),
>                var1 = col_double(),
>                ...
>            )
>
>There are a few other things that go into the file as well.
>
>Then I pick off the appropriate stuff from the environment in the other
>files:
>
>foo_alpha <- read_csv("alpha.csv", col_types =
>data_env$col_types_alpha)
>
>This seems to work, but it doesn't "feel" right to me.  (If this were
>Python,
>people would accuse me of being "non-pythonic").
>
>Hence, I'm seeking suggestions for the best practice for this kind of
>thing.
>
>BTW, I note that both the sources of data ("alpha", etc.) and the
>column types
>are more or less guaranteed to be static for the foreseeable future. 
>Hence,
>there really isn't much danger in just replicating the column-type
>definitions
>in each of the various files, which would obviate the need for the
>"000..."
>file.  In other words, this is mostly a style thing.
>
>Thanks for any advice you can provide.
>
>-- Mike
>
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-- 
Sent from my phone. Please excuse my brevity.