[R] Date formats

[Mikkel Grum]

Thanks to both of you. I tried to work on it, but the closest I could get was:

lifelse <- function (test, y, z) {
    iffy <- function(x) {
        if (x) {y} else {z}
    }
    lapply(test, iffy)
}

> lifelse(c(TRUE, FALSE), date -1, date)
[[1]]
[1] "2007-12-29"

[[2]]
[1] "2007-12-30"

> 
> d <- as.Date(c("1994-3-4", "1996-3-1"))
> lifelse(d > "1996-1-1", "1996-1-1", d)
[[1]]
[1] "1994-03-04" "1996-03-01"

[[2]]
[1] "1996-1-1"

> lifelse(d <= "1996-1-1", d, "1996-1-1")
[[1]]
[1] "1994-03-04" "1996-03-01"

[[2]]
[1] "1996-1-1"

Any attempts to unlist, paste, etc. to remove the list structure converted/removed the Date class.

Mikkel

----- Original Message ----
From: Peter Dalgaard <p.dalgaard at biostat.ku.dk>
To: Gabor Grothendieck <ggrothendieck at gmail.com>
Cc: Mikkel Grum <mi2kelgrum at yahoo.com>; r-help at stat.math.ethz.ch
Sent: Sunday, December 30, 2007 1:47:26 PM
Subject: Re: [R] Date formats

 Gabor Grothendieck wrote:
> Read the warning in ?ifelse
Yep.

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



      ____________________________________________________________________________________
Be a better friend, newshound, and 
know-it-all with Yahoo! Mobile.  Try it now.  http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ