If R does exactly what it says it does, why are you surprised, whether or not that is what other languages do? (Please excuse my fractured English). (Note: -8 = 1 + 3*(-3) = (-8 %% 3) + 3 * (-8 %/% 3 ), exactly as the Help excerpt you cited says)
Of course, one may always question the wisdom of whatever policy R chooses, but that gets into the bowels of what standards to follow, corner cases, and all that, about which I have nothing to say. My only point is the above. -- Bert On Mon, Dec 19, 2022 at 7:15 AM Göran Broström <g...@ehar.se> wrote: > > > Den 2022-12-19 kl. 15:41, skrev Martin Maechler: > >>>>>> Göran Broström > >>>>>> on Mon, 19 Dec 2022 14:22:00 +0100 writes: > > > > > I have a long vector x with five-digit codes where the > > > first digit of each is of special interest, so I extracted > > > them through > > > > >> y <- x %/% 10000 > > > > > but to my surprise y contained the value -1 in some > > > places. It turned out that x contains -1 as a symbol for > > > 'missing value' so in effect I found that > > > > >> -1 %/% 10000 == -1 > > > > > Had to check the help page for "%/%", and the first > > > relevant comment I found was: > > > > > "Users are sometimes surprised by the value returned". > > > > > No surprise there. Further down: > > > > > ‘%%’ indicates ‘x mod y’ (“x modulo y”) and ‘%/%’ > > > indicates integer division. It is guaranteed that > > > > > ‘ x == (x %% y) + y * (x %/% y) ’ (up to rounding > > > error) > > > > > I did expect (a %/% b) to return round(a / b), like > > > gfortran and gcc, > > > > What??? I cannot believe you. > > Well, you shouldn't, I generalized too far. > > > > No time for checking now, but I bet that > > 8 / 3 gives 2 and not 3 in C and Fortran > > (and hence gcc, etc) > > But compare -8 %/% 3 in R and -8 / 3 in C/Fortran. > > G, > > > > > > > > but instead I get floor(a / b) in > > > R. What is the reason for these different definitions? And > > > shouldn't R's definition be documented? > > > > > > > > > Thanks, Göran > > > > > ______________________________________________ > > > 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. > > ______________________________________________ > 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. > [[alternative HTML version deleted]] ______________________________________________ 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.
