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

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

But if you do mean to divide by max(x), I'll also vote for the prior

ROI <- function(x) {
if (length(x)==1) return(NA)
r=c(x[1], diff(x))/max(x)
return(r)}

As being about as quick and elegant as this can be done in R. 

M

On Aug 1, 2011, at 4:07 PM, "R. Michael Weylandt <michael.weylandt at gmail.com>" <michael.weylandt at gmail.com> wrote:

> 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
>> 
>> --
>> View this message in context: http://r.789695.n4.nabble.com/error-in-self-made-function-cannot-deal-with-objects-of-length-1-tp3710555p3710555.html
>> Sent from the R help mailing list archive at Nabble.com.
>> 
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