[R] Basic question - more efficient method than loop?

[Johannes Huesing]

GL <pflugg at shands.ufl.edu> [Mon, Jun 28, 2010 at 05:46:13PM CEST]:
> 
> I'm guessing there's a more efficient way to do the following using the index
> features of R. Appreciate any thoughts....

1st thought: ifelse()

> 
> for (i in 1:nrow(dbs1)){
>     if(dbs1$Payor[i] %in% Payor.Group.Medicaid) dbs1$Payor.Group[i] =
> "Medicaid"

within(dbs1, Payor.Group <- ifelse(Payor %in% Payor.Group.Medicaid, "Medicaid",
               ifelse( and so on ))

2nd thought: library(car); ?recode

3rd thought (untested and contrary to the spirit of R): 

lst <- list("Medicare", "Commercial", "Workers.Comp", etc. );

codePayor <- function(lst) {
  if (length(lst) == 0) ""
  else ifelse(dbs1$Payor %in% eval(parse(paste("Payor.Group", lst[[1]], sep="."))),
              lst[[1]],
              codePayor(lst[-1]))
}

dbs1$Payor.Group <- codePayor(lst)

-- 
Johannes Hüsing               There is something fascinating about science. 
                              One gets such wholesale returns of conjecture 
mailto:johannes at huesing.name  from such a trifling investment of fact.                
http://derwisch.wikidot.com         (Mark Twain, "Life on the Mississippi")