[R] Date formats
p.dalgaard at biostat.ku.dk
Sun Dec 30 11:47:26 CET 2007
Gabor Grothendieck wrote:
> Read the warning in ?ifelse
And, yes, it is annoying that ifelse() strips attributes, including
class, but it is one of those things that have been in the S languages
"forever", and nobody really wants to mess with. The fundamental issue
is that you need the result to be able to hold values from both of the
"yes" and the "no" arguments and there is no guarantee that that is
possible outside of the R base types.
You'd like to have things like these "work"
d <- as.Date(c("1994-3-4", "1996-3-1"))
ifelse(d > "1996-1-1", "1996-1-1", d)
ifelse(d <= "1996-1-1", d, "1996-1-1")
in the sense that the result is a Date object, but once you start
thinking about the details of how it _might_ work, you find that things
aren't all that simple. If there was a general mechanism for coercion
between classes, then maybe it could be done, but there isn't any.
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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