To cite ungroup in publications use:

Pascariu et al., (2018). ungroup: An R package for efficient estimation of smooth distributions from coarsely binned data. Journal of Open Source Software, 3(29), 937, https://doi.org/10.21105/joss.00937

Corresponding BibTeX entry:

  @Article{,
    title = {{ungroup}: An {R} package for efficient estimation of
      smooth distributions from coarsely binned data},
    author = {Marius D. Pascariu and Maciej J. Danko and Jonas Schoeley
      and Silvia Rizzi},
    journal = {Journal of Open Source Software},
    year = {2018},
    volume = {3},
    number = {29},
    pages = {937},
    doi = {10.21105/joss.00937},
  }