To cite package ‘Przewodnik’ in publications use:

  Biecek P (2016). _Przewodnik: Datasets and Functions Used in the Book
  'Przewodnik po Pakiecie R'_. R package version 0.16.12,
  <https://CRAN.R-project.org/package=Przewodnik>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {Przewodnik: Datasets and Functions Used in the Book 'Przewodnik po Pakiecie
R'},
    author = {Przemyslaw Biecek},
    year = {2016},
    note = {R package version 0.16.12},
    url = {https://CRAN.R-project.org/package=Przewodnik},
  }