Same basic philosophy as group_by_prepare(): lazy_dots comes in, list of data and vars (character vector) comes out.Source:
*_prepare() performs standard manipulation that is needed prior
to actual data processing. They are only be needed by packages
that implement dplyr backends.
distinct_prepare( .data, vars, group_vars = character(), .keep_all = FALSE, caller_env = caller_env(2), error_call = caller_env() ) group_by_prepare( .data, ..., .add = FALSE, .dots = deprecated(), add = deprecated(), error_call = caller_env() )