On May 20, 2013, at 2:09 PM, Alexandre Sieira wrote:
> I was trying to convert a vector of POSIXct into a list of POSIXct, However,
> I had a problem that I wanted to share with you.
>
> Works fine with, say, numeric:
>
>
>> v = c(1, 2, 3)
>> v
> [1] 1 2 3
>> str(v)
> num [1:3] 1 2 3
>> l = as.vector(v, mode="list")
>> l
> [[1]]
> [1] 1
>
> [[2]]
> [1] 2
>
> [[3]]
> [1] 3
>
>> str(l)
> List of 3
> $ : num 1
> $ : num 2
> $ : num 3
>
> If you try it with POSIXct, on the other hand…
>
>
>> v = c(Sys.time(), Sys.time())
>> v
> [1] "2013-05-20 18:02:07 BRT" "2013-05-20 18:02:07 BRT"
>> str(v)
> POSIXct[1:2], format: "2013-05-20 18:02:07" "2013-05-20 18:02:07"
>> l = as.vector(v, mode="list")
>> l
> [[1]]
> [1] 1369083728
>
> [[2]]
> [1] 1369083728
>
>> str(l)
> List of 2
> $ : num 1.37e+09
> $ : num 1.37e+09
>
> The POSIXct values are coerced to numeric, which is unexpected.
You may not have expected it, but that result is what is described: From the
help page for `as.vector`:
"For as.vector, a vector (atomic or of type list). All attributes are removed
from the result if it is of an atomic mode, ..."
And since POSIXct vectors _are_ of atomic mode, all of their attributes are
removed.
> is.atomic(as.POSIXct("2001-01-01") )
[1] TRUE
(I realize that this is a belated response, and that you and Jeff Newmiller are
continuing a correspondence on what I think appears to be a separate concern) ,
but I needed to go back to the first posting to figure out what the questions
were.
>
> The documentation for as.vector says: "The default method handles 24 input
> types and 12 values of type: the details of most coercions are undocumented
> and subject to change." It would appear that treatment for POSIXct is either
> missing or needs adjustment.
As in the case of factor-classed vectors, POSIXct-vectors are atomic mode.
Yours was a selective reading. (And you found a way around this with `as.list`.)
> is.atomic(factor("2001-01-01") )
[1] TRUE
--
David.
>
> Unlist (for the reverse) is documented to converting to base types, so I
> can't complain. Just wanted to share that I ended up giving up on
> vectorization and writing the two following functions:
>
>
> unlistPOSIXct <- function(x) {
> retval = rep(Sys.time(), length(x))
> for (i in 1:length(x)) retval[i] = x[[i]]
> return(retval)
> }
>
> listPOSIXct <- function(x) {
> retval = list()
> for (i in 1:length(x)) retval[[i]] = x[i]
> return(retval)
> }
>
> Is there a better way to do this (other than using *apply instead of for
> above) that better leverages vectorization? Am I missing something here?
>
> Thanks!
>
>
--
David Winsemius
Alameda, CA, USA
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