[R] the first. from SAS in R

[Joel]

Is there any similar function in R to the first. in SAS?

What it dose is:

Lets say we have this table:

  a b  c
  1 1  5
  1 0  2
  2 0  2
  2 0 NA
  2 9  2
  3 1  3


and then I want do to do one thing the first time the number 1 appers in a
and something else the secund time 1 appers in a and so on.

so 

something similar to:

if first.a {
 a$d<-1
}else{
 a$d<-0
}

This would give me

  a b  c b
  1 1  5 1
  1 0  2 0
  2 0  2 1
  2 0 NA 0
  2 9  2 0
  3 1  3 1

Is there such a function in R or anything similar?


thx

//Joel

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