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 ;)
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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