On Fri, May 19, 2017 at 6:38 AM, S Ellison <s.elli...@lgcgroup.com> wrote: >> 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'.
That's not TRUE ;) sqlite> select (3 > 2) OR NULL; 1 sqlite> select (4 < 3) AND NULL; 0 Hadley -- http://hadley.nz ______________________________________________ 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.
