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

[bjmjarrett]

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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