https://ngriffiths21.r-universe.dev/grouprhttps://ngriffiths21.r-universe.dev/api/packages/grouprhttps://ngriffiths21.r-universe.dev/groupr/groupr.pdfhttps://ngriffiths21.r-universe.dev/groupr/doc/manual.htmlhttps://ngriffiths21.r-universe.dev/groupr/NEWShttps://ngriffiths21.r-universe.dev/groupr/NEWS.txthttps://ngriffiths21.r-universe.dev/groupr/citationhttps://ngriffiths21.r-universe.dev/groupr/citation.txthttps://ngriffiths21.r-universe.dev/groupr/citation.cffhttps://ngriffiths21.r-universe.dev/groupr/doc/introduction.Rmdhttps://ngriffiths21.r-universe.dev/articles/groupr/introduction.html