> TRUE & FALSE is FALSE but TRUE & TRUE is TRUE, so TRUE & NA could be
> either TRUE or FALSE and consequently is NA.
>
> OTOH FALSE & (anything) is FALSE so FALSE & NA is FALSE.
>
> As I said *think* about it; don't just go with your immediate knee-jerk
> (simplistic) reaction.
Hmm... not sure that was quite fair to the OP. Yes, FALSE & <anything> ==
FALSE. But 'NA' does not mean 'anything'; it means 'missing' (see ?'NA'). It is
much less obvious that FALSE & <missing> should generate a non-missing value.
SQL, for example, generally takes the view that any expression involving
'missing' is 'missing'.
And R's behaviour can look odd if the vagaries of real data intervene:
b1 <- c(A=TRUE, C=FALSE)
b2 <- c(A=FALSE, B=FALSE, C=TRUE)
b1['B'] & b2['B']
#Which returns
# <NA>
# FALSE
which - particularly since it appears without warning - is not an obviously
sensible outcome.
I am not suggesting a change to R's logical operations, which have clearly been
thought through (that is evident from NA&FALSE == FALSE&NA == FALSE). But R's
behaviour looks to me like a choice among difficult alternatives, rather than
the only possible choice. I'd give the OP some credit for that.
S Ellison
S Ellison
*******************************************************************
This email and any attachments are confidential. Any use...{{dropped:8}}
______________________________________________
R-help@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.
