I couldn't resist, either...
> From: Henrik Bengtsson
>
> Hmm,
>
> couldn't resists:
>
> > X <- NA
> > is.logical(X)
> [1] TRUE
> > (X == TRUE)
> [1] NA
>
> > "==.MaybeNA" <- function(e1, e2) { !is.na(e1) && (e1 == e2) }
> > X <- structure(NA, class="MaybeNA")
> > is.logical(X)
> [1] TRUE
> > (X == TRUE)
> [1] FALSE
>
> Ta da ;)
But anything compared to NA should result in NA!
Andy
> Henrik
>
> PS. It might be worth mentioning base::isTRUE() when we're
> already at it. DS.
>
>
> On Thu, Aug 14, 2008 at 3:07 PM, Rolf Turner
> <[EMAIL PROTECTED]> wrote:
> >
> > I just noticed a certain ``usage'' in a recent posting, and couldn't
> > restrain my self from commenting. The usage was of the form
> >
> > ``if(X==TRUE)''
> >
> > where X was a logical variable.
> >
> > This sort of thing is brought to you by your Department of
> Redundancy
> > Department. The ``==TRUE'' bit is irrelevant, incompetent,
> and immaterial,
> > as Perry Mason used to say. The value of X==TRUE is
> exactly the same as
> > the value of X when X is a logical variable. If X is not a
> logical variable
> > a lot of strange things can happen, depending on the nature of X.
> >
> > It is safer and takes 6 fewer key strokes to use ``if(X)''.
> So why not
> > do that, eh?
> >
> > cheers,
> >
> > Rolf Turner
> >
> > P. S. The example that triggered this post actually used
> ``if(X==T)''.
> > This is doubly dangerous since ``T'' can be overwritten. If it was
> > overwritten you'd get toadally wrong answers. E.g., suppose you had
> > set
> >
> > T <- FALSE # !!!
> >
> > ***ALWAYS USE ``TRUE'' AND ``FALSE'' FOR LOGICAL VALUES.
> > DO NOT USE ``T'' AND ``F''.***
> >
> >
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> >
>
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