error in self-made function - cannot deal with objects of length = 1

Just jumping into this, but does the ROC(x, type="discrete") function of either the TTR or caTools (can't remember which) work if you need a prebuilt function?

Also, why are you dividing by the max value? That seems a funny way to calculate ROC...

On Aug 1, 2011, at 3:14 PM, bjmjarrett <bjmjarrett at gmail.com> wrote:

I have a function to calculate the rate of increase (the difference between
the value and the previous value divided by the total number of eggs in a
year) of egg production over the course of a year:

rate <- function(x){
     storage <- matrix(nrow=length(x),ncol=1)
     storage[1,] <- x[1] / max(x) # as there is no previous value
     for( i in 2:length(x)){
     p <- i - 1
     storage[i,] <- ((x[i] - x[p] / max(x))
     }
     return(storage)
}

However, as it requires the subtraction of one term with the previous term
it fails when dealing with objects with length = 1 (when only one reading
has been taken in a year). I have tried adding an ifelse() function into
`rate' with NA added for length 1: 

rate <- function(x){
  storage <- matrix(nrow=length(x),ncol=1)
  ifelse(length(x)==1,storage[1,] <- NA,{
  storage[1,] <- x[1]/max(x)
  for(i in 2:length(x)){
      p <- i-1
      storage[i,] <- ((x[i] - x[p]) / max(x))
      }
  })
  return(storage)
  }

but I end up with this error when I try and use the above function in
tapply():

Error in ans[!test & !nas] <- rep(no, length.out = length(ans))[!test & : 
replacement has length zero

Thanks in advance,

Ben

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