[R] Recoding several variables into one use the most recent data

[David Winsemius]

On Jun 27, 2011, at 12:56 PM, Christopher Desjardins wrote:

> Hi,
> I have the following data management issue. I am trying to combine  
> multiple
> years of ethnicity data into one variable called ethnic. The data  
> looks
> similar to the following
>
> id    ethnic07    ethnic08   ethnic09    ethnic10
> 1          1              1             1                1
> 2          1              1             2                2
> 3          3              4             4                NA
> 4          2              3           NA                NA
>
> So, what I'd like to do is create a variable called 'ethnic' and I'd  
> like to
> have this variable be filled with the most recent data available. So
> ethnic10 would have the highest priority, then ethnic09, followed by
> ethnic08, and finally ethnic07.  So the ethnic variable based on the  
> data
> above would look like the following:
>
> ethnic
>   1
>   2
>   4
>   3
>
rd.txt <- function(txt, header=TRUE, ...) {
      rd <- read.table(textConnection(txt), header=header, ...)
        closeAllConnections()
      rd }

 > tail_noNA <- function(x,n) tail(x[!is.na(x)], n)
 > tail_noNA(c(1,2,3,NA),1)
[1] 3
 > dat <-rd.txt("id    ethnic07    ethnic08   ethnic09    ethnic10
+ 1          1              1             1                1
+ 2          1              1             2                2
+ 3          3              4             4                NA
+ 4          2              3           NA                NA")
 > apply(dat, 1, tail_noNA, 1)
[1] 1 2 4 3

 > as.matrix(apply(dat, 1, tail_noNA, 1))
      [,1]
[1,]    1
[2,]    2
[3,]    4
[4,]    3


> I thought an ifelse() statement might work but I seem to be writing  
> over my
> data every time I do this.
>
> Thanks,
> Chris
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT