This function is deprecated as of choroplethr version 3.0.0. Please use ?get_acs_data instead. The last version of choroplethr in which this functions worked was version 2.1.1, which can be downloaded from CRAN here: http://cran.r-project.org/web/packages/choroplethr/index.html
get_acs_df(...)
All arguments are ignored.