If you supply vectors for both file_name and year, then the vectors are paired and each file_name/year pair is downloaded.
For example, file_name = c("EPH, GHB"), year = c("2009-2010", "2011-2012") will download "EPH_F.XPT" and "EPH_G.XPT".
In other words, the function does not download every possible combination of file_name and year.You can specify file names in several formats. In order of specificity:
You can supply the complete filename: "EPH_F.XPT"
You can supply the filename without an extension: "EPH_F"
You can supply the filename without a suffix: "EPH", year = "2009-2010"
If you are loading the same file across multiple years, you must supply the filename without a suffix so
that the correct suffix for each year can be used.
This function returns either a list or a data frame. If you load multiple files, the return value will always be a list. This is because
the columns may not match in between files.
If you load one file, the result will be a data frame.