R equivalent of .first or .last sas operator

Question

Does anybody know what is the best R alternative to SAS first. or last. operators? I did find none.

SAS has the FIRST. and LAST. automatic variables, which identify the first and last record amongst a group with the same value with a particular variable; so in the following dataset FIRST.model and LAST.model are defined:

Model,SaleID,First.Model,Last.Model
Explorer,1,1,0
Explorer,2,0,0
Explorer,3,0,0
Explorer,4,0,1
Civic,5,1,0
Civic,6,0,0
Civic,7,0,1

Answer 1

It sounds like you're looking for !duplicated, with the fromLast argument being FALSE or TRUE.

d <- datasets::Puromycin

d$state
# [1] treated   treated   treated   treated   treated   treated   treated  
# [8] treated   treated   treated   treated   treated   untreated untreated
#[15] untreated untreated untreated untreated untreated untreated untreated
#[22] untreated untreated
#Levels: treated untreated
!duplicated(d$state)
# [1]  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
#[13]  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
!duplicated(d$state,fromLast=TRUE)
# [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE
#[13] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE

There are some caveats and edge-case behaviors to this function, which you can find out through the help files (?duplicated).