[R] treating integer(0) and NULL in conditions and loops

[Adams, Jean]

To reframe the problem ... the issue is not with the function nchar() (or
whatever), it's with the input value rz being null.  I suggest you build
into the loop whatever actions/outputs you want when rz is NULL.

for (i in 1:10){
  if (is.null(rz)) {
    # do something here
  } else {
    if (nchar(rz)>6) {
      # ...
    }
    if (nchar(a[i])+nchar(rz))<6) {
      # ...
    }
    if (nchar(rz)+nchar(a[i+1]>6) {
      # ...
    }
  }
}

Jean


On Fri, Mar 11, 2016 at 8:55 AM, Jan Kacaba <jan.kacaba at gmail.com> wrote:

> Hello, I have following problem in loops. It occurred to me multiple times
> bellow is an example.  Inside if() I have sometimes function f(x) which may
> return integer(0).  If I test f(x)>1 and f(x)=integer(0) I get error. Maybe
> it can be solved more eloquently without loop or swithces. I don't know.
>
> Example:
>
> a=c("ab","abc","abcd","abcde","abcdefghjk") # vector from which new strings
> will be constructed
> svec=NULL # vector of string
> rz=NULL # string
>
> for (i in 1:10){
> if (nchar(rz)>6){
>   svec[i]=rz
>   rz=NULL
> }
>
> if (nchar(a[i])+nchar(rz))<6){
>   rz=paste(rz,a[i])
> }
>
> if (nchar(rz)+nchar(a[i+1]>6){
>   svec[i]=rz
>   rz=NULL
> }
> }
>
> I'm not interested how to treat nchar() function in particular but general
> function. One solution which comes to mind is to redefine function for
> example nchar() function like this:
>
> new.nchar=function(x){
> if (length(nchar(rz))==0){z=0}
> if (length(nchar(rz))>0){z=nchar(rz)}
> return(z)
> }
>
> Is it correct way of doing this or is there a better way without the need
> of redefining new function?
> <derek>
>
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>
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