[R] R first.id last.id function error

[Gabor Grothendieck]

A slightly easier way to construct first and last if the vector x is
sorted (as is assumed in SAS) is:

   first <- !duplicated(x)
   last <- !duplicated(x, fromLast = TRUE)

where the fromLast= argument is added in R 2.6.0.


On 9/7/07, Gerard Smits <g_smits at verizon.net> wrote:
> Hi R users,
>
> I have a test dataframe ("file1," shown below) for which I am trying
> to create a flag for the first and last ID record (equivalent to SAS
> first.id and last.id variables.
>
> Dump of file1:
>
>  > file1
>    id rx week dv1
> 1   1  1    1   1
> 2   1  1    2   1
> 3   1  1    3   2
> 4   2  1    1   3
> 5   2  1    2   4
> 6   2  1    3   1
> 7   3  1    1   2
> 8   3  1    2   3
> 9   3  1    3   4
> 10  4  1    1   2
> 11  4  1    2   6
> 12  4  1    3   5
> 13  5  2    1   7
> 14  5  2    2   8
> 15  5  2    3   5
> 16  6  2    1   2
> 17  6  2    2   4
> 18  6  2    3   6
> 19  7  2    1   7
> 20  7  2    2   8
> 21  8  2    1   9
> 22  9  2    1   4
> 23  9  2    2   5
>
> I have written code that correctly assigns the first.id and last.id variabes:
>
> require(Hmisc)  #for Lags
> #ascending order to define first dot
> file1<- file1[order(file1$id, file1$week),]
> file1$first.id <- (Lag(file1$id) != file1$id)
> file1$first.id[1]<-TRUE      #force NA to TRUE
>
> #descending order to define last dot
> file1<- file1[order(-file1$id,-file1$week),]
> file1$last.id  <- (Lag(file1$id) != file1$id)
> file1$last.id[1]<-TRUE       #force NA to TRUE
>
> #resort to original order
> file1<- file1[order(file1$id,file1$week),]
>
>
>
> I am now trying to get the above code to work as a function, and am
> clearly doing something wrong:
>
>  > first.last <- function (df, idvar, sortvars1, sortvars2)
> +   {
> +   #sort in ascending order to define first dot
> +   df<- df[order(sortvars1),]
> +   df$first.idvar <- (Lag(df$idvar) != df$idvar)
> +   #force first record NA to TRUE
> +   df$first.idvar[1]<-TRUE
> +
> +   #sort in descending order to define last dot
> +   df<- df[order(-sortvars2),]
> +   df$last.idvar  <- (Lag(df$idvar) != df$idvar)
> +   #force last record NA to TRUE
> +   df$last.idvar[1]<-TRUE
> +
> +   #resort to original order
> +   df<- df[order(sortvars1),]
> +   }
>  >
>
> Function call:
>
>  > first.last(df=file1, idvar=file1$id,
> sortvars1=c(file1$id,file1$week), sortvars2=c(-file1$id,-file1$week))
>
> R Error:
>
> Error in as.vector(x, mode) : invalid argument 'mode'
>  >
>
> I am not sure about the passing of the sort strings.  Perhaps this is
> were things are off.  Any help greatly appreciated.
>
> Thanks,
>
> Gerard
>        [[alternative HTML version deleted]]
>
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