R help - Mar 2016 - treating integer(0) and NULL in conditions and loops

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>

	[[alternative HTML version deleted]]

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>
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

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:
> 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>
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]