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

[R. Michael Weylandt <michael.weylandt@gmail.com>]

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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