The base functionality here is simple pattern-matching on keywords
in ps_data_version. This simple pattern-matching is in base R. I
assume the user has some familiarity with the types of data included in
this package.
The searching is done by category included in the ps_data_version data.
Users may want to just minimally run ps_version() with no argument
specified to see for themselves what's in it. Typing
unique(ps_data_version$category) may also get them started.
The user can consider this a companion function to ps_cite().
Whereas ps_cite() will return the appropriate citation
to use in the bibliography, it may not tell them the version number at all.
For example, the classic and suggested citations for the Correlates of War
National Material Capabilities data are too Singer et al. (1972) and Singer
(1987), though the data included in this package are about 30 years older
than the most recent citation of the two.
The information communicated here can/should be included alongside a
parenthetical citation. For example, the contiguity data are
quite a bit more current than the suggested citation to Stinnett et al.
(2002). Thus, a user may want to cite the data in their paper
as something like (Stinnett et al. 2002, v. 3.2).