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,
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.
