[R] the first. from SAS in R

David Winsemius
Tue, 23 Nov 2010 14:12:09 -0000

On Nov 23, 2010, at 8:33 AM, Joel wrote:

>
> 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
> }
>

The duplicated function which returns a logical vector with those
features can easily be coerced to numeric.

df$d <- as.numeric(!duplicated(df$a))


I was a bit puzzled about my failure to get coercion by the method
which I thought was supposed to work, namely adding 0.

df$e <- !duplicated(df$a)+0  # does not coerce

df$e <- 0 + !duplicated(df$a) # pre-adding 0 does coerce

Maybe the rules on coercion were amended.

--
David

> 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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>
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David Winsemius, MD
West Hartford, CT