[R] function on factors - how best to proceed

[Gustaf Rydevik]

On 9/19/07, Gustaf Rydevik <gustaf.rydevik at gmail.com> wrote:
> On 9/19/07, Karin Lagesen <karin.lagesen at medisin.uio.no> wrote:
> > "Gustaf Rydevik" <gustaf.rydevik at gmail.com> writes:
> >
> >
> > > The second warning message tells you that:
> > >  2: the condition has length > 1 and only the first element will be
> > > used in: if (terminus > origin)
> > >
> > > You are comparing two vectors,  which generate a vector of TRUE/FALSE values.
> > > The "if" statement need a single TRUE/FALSE value.
> > > Either use a for loop:
> > > for (i in 1:nrow(terminus)) {if terminus[i]> origin[i]...}
> > > or a nested ifelse statement (which is recommendable on such a big data set).
> >
> > Thankyou for your reply! I will certainly try the numeric thing.
> >
> > Now, for the vector comparison. I can easily see how you would do a
> > for loop here, but I am unable to see how a nested ifelse statement
> > would work. Could you possibly give me an example?
> >
> > Thankyou again for your help!
> >
> > Karin
> > --
> > Karin Lagesen, PhD student
> > karin.lagesen at medisin.uio.no
> > http://folk.uio.no/karinlag
> >
>
> You replace each instance of "if" with ifelse, inserting a comma after
> the logical test, and instead of the else statement.  The end result
> would become (if I've not made a mistake):
>
> _____
> replicator<-rep(c("LEFT","RIGHT"),50)
> terminus<-rnorm(100)
> origin<-rnorm(100)
> begin<-rnorm(100)
> length<-sample(1:100,100,replace=T)
>
> d<-ifelse(terminus>origin,
>         +ifelse(replicator=="LEFT",-((origin-begin))%%length),(begin-origin)),
>         +ifelse(replicator=="LEFT",(origin-begin),-((begin-origin)%%length))
>         +)
>
> /Gustaf
>
>
> --
> Gustaf Rydevik, M.Sci.
> tel: +46(0)703 051 451
> address:Essingetorget 40,112 66 Stockholm, SE
> skype:gustaf_rydevik
>

Sorry, forgot to remove the plusses, and had a parenthesis wrong...

______________
replicator<-rep(c("LEFT","RIGHT"),50)
terminus<-rnorm(100)
origin<-rnorm(100)
begin<-rnorm(100)
length<-sample(1:100,100,replace=T)

d<-ifelse(terminus>origin,
      ifelse(replicator=="LEFT",-((origin-begin)%%length),(begin-origin)),
      ifelse(replicator=="LEFT",(origin-begin),-((begin-origin)%%length))
      )
___________


best,

Gustaf
-- 
Gustaf Rydevik, M.Sci.
tel: +46(0)703 051 451
address:Essingetorget 40,112 66 Stockholm, SE
skype:gustaf_rydevik