intersect()
union()
setdiff()
vector()
NA
matrix()
list()
NULL
data.frame()
if
else
ifelse()
dplyr::if_else()
data.table::fifelse()
dplyr::case_when()
data.table::fcase()
https://cran.r-project.org/
https://rstudio.com/products/rstudio/download/