R equivalent of Stata local or global macros

Question

I am a Stata user trying to learn R.

I have a couple of lengthy folder paths which, in my Stata code, I stored as local macros. I have multiple files in both those folders to use in my analysis.

I know, in R, I can change the working directory each time I want to refer to a file in one of the folders but it is definitely not a good way to do it. Even if I store the folder paths as strings in R, I can't figure out how to refer to those. For example, in Stata I would use `folder1'.

I am wondering if trying to re-write Stata code line by line in R is not the best way to learn R.

Can someone please help?

Answer 1

First, as a former Stata user, let me recommend R for Stata Users. There is also this article on Macros in R. I think @Nick Cox is right that you need to learn to do things more differently. But like you (at least in this case), I often find myself starting a new task with my prior knowledge of how to do it in Stata and going from there. Sometimes I find the approaches are similar. Sometimes I can make R act like Stata when a different approach would be better (e.g., loops vs. vectorization).

I'm not sure if I will capture your question with the following, but let me try.

In Stata, it would be common to write:

global mydata "path to my data directory/"

To import the data, I would just type:

insheet using "${mydata}myfile.csv"

As a former Stata user, I want to do something similar in R. Here is what I do:

mydata <- "path to my data directory/"

To import a csv file located in this directory and create a data frame called myfile, I would use:

myfile <- read.csv(paste(mydata, "myfile.csv", sep=""))

or more efficiently...

myfile <- read.csv(paste0(mydata, "myfile.csv"))

I'm not a very efficient R user yet, so maybe others will see some flaws in this approach.

Answer 2

Maybe you want file.path()?

a <- "c:"
b <- "users"
c <- "charles"
d <- "desktop"

setwd(file.path(a,b,c,d))
getwd()
#----
[1] "c:/users/charles/desktop"

You can wrap source or read.XXX or whatever else around that to do what you want.

Answer 3

I'm guessing from context that the term "local" when applied to files means that they have been loaded into memory for efficiency purposes? If so, then you need to realize that pretty much all ordinary R objects are handled that way. See ?read.table and ?load. The only way data can remain non-local is to have it reside in a database that has an interface package that supports SQL queries or use specialized packages such as ff or bycol.

Other than that and Chase's idea to use file.path(), any reference to files or connections is done using the proper read/load/scan functions to which character values are given as (variously named) arguments. You can see a variety of low-level functions with ?file and perhaps following some of the additional links from that help page. You could store one or more results of a file.path construction in a character vector which could be named for easy reference.

 pathvecs <- c(User= "~/", hrtg="~/Documents/Heritage/")
 pathvecs
#                   User                    hrtg 
#                   "~/" "~/Documents/Heritage/" 
pathvecs["hrtg"]
#                   hrtg 
#"~/Documents/Heritage/"