> > Is there any similar function in R to the first. in SAS?
>     ?duplicated
> 
>     a$d <- ifelse( duplicated( a$a ), 0 , 1 )
> 
>     a$d.2 <- as.numeric( !duplicated( a$a ) )

Actually, duplicated does not duplicate SAS' first. operator, though it 
may suffice for the OP's needs.

To illustrate, let's start with a dataframe of 3 key columns and some data 
in x:
tt <- data.frame(k1 = rep(1:3, each=10), k2 = rep(1:5, each=2, times=3), 
k3=rep(1:2, times=15), x = 1:30)

# Try to mimic what the following SAS datastep would do, 
# assuming 'tt' is already sorted:
#       data foo;
#         set tt;
#         by k1, k2;
#         put first.k1=, first.k2=;
#       run;

# SAS' first. operations would result in these values:
tt$sas.first.k1 <- rep(c(1, rep(0,9)), 3)
tt$sas.first.k2 <- rep(1:0, 15)

# R duplicated() returns these values.  You can see they 
# are the same for k1, but dissimilar after row 10 for k2.
tt$duplicated.k1 <- 0+!duplicated(tt$k1)
tt$duplicated.k2 <- 0+!duplicated(tt$k2)

# I've found I need to lag a column to mimic SAS' first. 
# operator, thusly, though perhaps someone else knows 
# differently.  Note this does not work on unordered 
# dataframes!
lag.k1 <- c(NA, tt$k1[1:(nrow(tt) - 1)])
tt$r.first.k1 <- ifelse(is.na(lag.k1), 1, tt$k1 != lag.k1)

lag.k2 <- c(NA, tt$k2[1:(nrow(tt) - 1)])
tt$r.first.k2 <- ifelse(is.na(lag.k2), 1, tt$k2 != lag.k2)

Mimicking SAS' last. operation can be done in a similar manner, by 
anti-laging the column of interest and changing the comparisons somewhat.

Enjoy the days,
cur
-- 
Curt Seeliger, Data Ranger
Raytheon Information Services - Contractor to ORD
seeliger.curt@epa.gov
541/754-4638

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