[R] if syntax error :(

[Gabor Grothendieck]

On 6/13/06, Rolf Turner <rolf at erdos.math.unb.ca> wrote:
> H. Paul Benton wrote:
>
> > Umm sorry to bother everyone again but I'm having trouble with my if
> > statement. I come from a perl background so that's probably my problem! :)
> > So here is my code:
> >
> > if (any(lgAB>4) | any(lgAB<-4)){
> >       freq_AB<-hist(lgAB, type="o", plot=F)
> >       else
> >       freq_AB<-hist(lgAB, breaks=br,type ="o", plot=F)
> > }
> >
> > And I get
> > > source("E:/R/GMDA-1.1.R")
> > Error in parse(file, n = -1, NULL, "?") : syntax error at
> > 11:             freq_AB<-hist(lgAB, type="o", plot=F)
> > 12:             else
> > >
>
> No-one yet has pointed out the following problem, which, while not be
> a syntax error as such, will cause you headaches:
>
>        if (any(lgAB>4) | any(lgAB<-4)){
>                              ^^^^^^^
>
> This assigns the value 4 to lgAB (which is presumably NOT what
> you want to do).  You want ``any(lgAB < -4)''.
>
> General rule:  Put in spaces around operators --- it makes the
> code (much) more readable and avoids unintended consequences.
>
> Another infelicity in your code: ``plot=F''.  Use ``plot=FALSE''.
> (Note that the symbols ``F'' and ``T'' are assignable, *unlike*
> ``TRUE'' and ``FALSE''.)
>

In fact if we are going to improve the code we could write it more
compactly and in a way which shows more clearly that the if
is only involved in setting breaks like this:

freq_AB <-  hist(lgAB,  type = "o", plot = FALSE,
  breaks = if (any(abs(lgAB) > 4)) "Sturges" else br)