R help - Aug 2011 - error in self-made function - cannot deal with objects of length = 1

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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bjmjarrett wrote:
> 
> ...
> 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
> 
> 
ifelse is for vector arguments.
You should use if(....) {.......} else {.....}

But why not just

c(x[1], diff(x))/max(x)

Berend

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> But why not just
> c(x[1], diff(x))/max(x)
So simple! Thank you ever so much Berend.

Best wishes,

Ben




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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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> View this message in context:
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> Sent from the R help mailing list archive at Nabble.com.
> 
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