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.

A BibTeX entry for LaTeX users is

  @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://doi.org/10.32614/RJ-2017-016},
    doi = {10.32614/RJ-2017-016},
  }