Error(s) in re-building vignettes

[nfrerebeau]

See the problems shown on https://cran.r-project.org/web/checks/check_results_tabula.html.

These can be reproduced by checking with --as-cran using a very current r-devel (r77865 or later), which makes data.frame() and read.table() use a stringsAsFactors = FALSE default, which is planned to become the new default for the upcoming R 4.0.0.

See https://developer.r-project.org/Blog/public/2020/02/16/stringsasfactors/index.html for more information about this change.

Fix the package to work with both the old and new default In principle, this can easily be achieved by adding stringsAsFactors = TRUE to the relevant calls to data.frame() or read.table() [or other read.* function calling read.table()], but only do this if the sort order used in the string to factor conversion really does not matter (see the blog post about the locale dependence of the conversion). Otherwise, change to create the factors with explicitly given levels.

Correct before 2020-03-20 to safely retain the package on CRAN.