To cite package 'rio' in publications use:

Chung-hong Chan, Geoffrey CH Chan, Thomas J. Leeper, and Jason Becker (2017). rio: A Swiss-army knife for data file I/O. R package version 0.5.5.

Corresponding BibTeX entry:

  @Manual{,
    title = {rio: A Swiss-army knife for data file I/O},
    author = {Chung-hong Chan and Geoffrey CH Chan and Thomas J. Leeper
      and Jason Becker},
    year = {2017},
    note = {R package version 0.5.5},
  }