To cite pdp in publications use:

Brandon M. Greenwell (2017). pdp: An R Package for Constructing Partial Dependence Plots. The R Journal, 9(1), 421--436. URL https://journal.r-project.org/archive/2017/RJ-2017-016/index.html.

Corresponding BibTeX entry:

  @Article{,
    title = {pdp: An R Package for Constructing Partial Dependence
      Plots},
    author = {Brandon M. Greenwell},
    journal = {The R Journal},
    year = {2017},
    volume = {9},
    number = {1},
    pages = {421--436},
    url =
      {https://journal.r-project.org/archive/2017/RJ-2017-016/index.html},
  }