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treating integer(0) and NULL in conditions and loops

3 messages · derek, Adams, Jean, William Dunlap

Original
derek
# 
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>
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:

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      William Dunlap
    

    

      
      #
    

  


  

      
I would suggesting using "" instead of NULL for rz, throughout this code.

(I would also suggest making sure the code can be copied into R without
causing a syntax error before posting the request for help.)

Bill Dunlap
TIBCO Software
wdunlap tibco.com

        
On Fri, Mar 11, 2016 at 9:10 AM, Adams, Jean <jvadams at usgs.gov> wrote: