Alternatively, x can be a list of data frames or a string vector of
object names, to write many tables in one call. The resulting files are named
automatically, similar to file = NULL.
The default value file = NULL uses the name of x as a filename,
so a data frame called survey.uk will be written to a file called
survey_uk.csv (when underscore = TRUE) or survey.uk.csv
(when underscore = FALSE).
The special value file = "" prints the data frame in the console,
similar to write.csv.