If you ran execGRASS("g.extension", extension="r.boxplot", operation="add"),
the add-on will not be found until you restart the R session in RStudio
(parseGRASS caches all *.bat found the first time it is used on Windows). GRASS
extensions are installed in GRASS, not R, but can be installed
It is a GRASS addon, install as per:
https://grass.osgeo.org/download/addons/
https://grass.osgeo.org/grass83/manuals/g.extension.html
https://grass.osgeo.org/grass83/manuals/addons/r.boxplot.html
--
Roger Bivand
Emeritus Professor
Norwegian School of Economics
Postboks 3490 Ytre Sandviken,
