Re: [R] POSIXlt converted to POSIXct in as.data.frame()
Thank you, Spencer.
It *does* depend on the exact environment such as timezone,
locale, ???
In my (Linux) setup, I can reproduce Rogers' 1-off problem
using exactly your (Spencer's) R script.
Carefully considering the warning in ?POSIXlt,
and using Sys.getenv(TZ) to see that I had no timezone set,
I've used
Sys.putenv(TZ = MET)
to correctly set my timezone, but that still did not help,
so I tried
Sys.putenv(TZ = UTC+1)
and that *did* solve the problem.
Interestingly, even
Sys.putenv(TZ = )
does solve the problem for me.
Here is small function, derived from your codes,
which is useful for testing these settings:
tstD - function(x.Plt = strptime(paste(9:13, Nov 2006), format=%d %b %Y))
{
## Purpose: Check POSIXlt - Dataframe (i.e. - POSIXct) - Date conversion
## --
## Arguments: x.Plt: a correct POSIXlt object
## --
## Author: Martin Maechler, Date: 15 Nov 2006, 10:16
stopifnot(inherits(x.Plt, POSIXlt))
d0 - as.Date(x.Plt)
if(isTRUE(getOption(verbose))) {
cat(as.Date(*): ); str(d0) }
dd - data.frame(x.Plt)
## - column converted to P..ct -- definitely needed and desired
dDate - as.Date(dd[,x.Plt])
stopifnot(dDate - d0 == 0)
## else
OK
}
SpG == Spencer Graves [EMAIL PROTECTED]
on Sun, 12 Nov 2006 08:26:09 -0800 writes:
SpG I'm not qualified to say much about POSIX, but I haven't seen a
SpG reply to this in almost 3 days, so I'll offer a comment in the hopes
SpG that it might be useful or that someone else might correct any
SpG misstatement I might make:
SpG First, I didn't find a discrepancy.
sessionInfo()
SpG R version 2.4.0 (2006-10-03)
SpG i386-pc-mingw32
SpG locale:
SpG LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
SpG States.1252;LC_MONETARY=English_United
SpG States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
SpG attached base packages:
SpG [1] methods stats graphics grDevices utils
datasets
SpG [7] base
SpG I used the following modification extension of your example:
SpG my_POSIXlt - strptime(c(11-09-2006, 11-10-2006, 11-11-2006,
SpG11-12-2006, 11-13-2006), %m-%d-%Y)
SpG str(my_POSIXlt)
SpG class(my_POSIXlt)
SpG my_Date - as.Date(my_POSIXlt)
SpG str(my_Date)
SpG myCharacters - format(my_Date)
SpG class(myCharacters)
SpG my_DF - data.frame(my_POSIXlt)
SpG str(my_DF)
SpG DF_Date - as.Date(my_DF$my_POSIXlt)
SpG str(DF_Date)
SpG DF_Date
SpG all.equal(DF_Date, my_Date)
SpG # TRUE
SpG The data.frame function converts POSIXlt, which is a list, to
SpG POSIXct, which is a numeric vector with attributes:
attributes(my_DF$my_POSIXlt)
SpG $class
SpG [1] POSIXt POSIXct
SpG $tzone
SpG [1]
is.numeric(my_DF$my_POSIXlt)
SpG [1] TRUE
SpG If you are getting a day shift, I would guess that you might have
SpG a different version of some of the software or a difference in your
SpG locale. I just did 'update.packages()' yesterday, so if I'm out of
date
SpG on something, I hope someone will help me understand and fix the
problem.
SpG Beyond this, have you reviewed the ?POSIXt help file plus Gabor
SpG Grothendieck and Thomas Petzoldt. R help desk: Date and time classes
in
SpG R. R News, 4(1):29-32, June 2004 (available from www.r-project.org -
SpG Newsletter)?
SpG Hope this helps.
SpG Spencer Graves
SpG Roger Bivand wrote:
In trying to use as.Date(), I've come across the conversion of POSIXlt
to
POSIXct when a POSIXlt variable is included in a data frame:
my_POSIX - strptime(c(11-09-2006, 11-10-2006, 11-11-2006,
11-12-2006, 11-13-2006), %m-%d-%Y)
str(my_POSIX)
my_Date - as.Date(my_POSIX)
str(my_Date)
data - format(my_Date)
str(data)
my_DF - data.frame(my_POSIX)
str(my_DF)
DF_Date - as.Date(my_DF$my_POSIX)
str(DF_Date)
DF_Date
The consequence (for my LC_TIME and machine time zone) is that when
as.Date() is applied to the data frame column, it dispatches on
as.Date.POSIXct() not as.Date.POSIXlt(), causing a day shift (actually
60
minutes, but because as.Date.POSIXct() says floor(), it ends up being a
whole day). Should data.frame() be changing POSIXlt to POSIXct?
Yes, that was at least a main idea of POSIXct: it can be dealt
with like a numeric vector and hence fits ideally into a data frame.
As as.data.frame.POSIXlt() is written, it says:
as.data.frame.POSIXlt
function (x, row.names = NULL, optional = FALSE, ...)
{
value - as.data.frame.POSIXct(as.POSIXct(x), row.names,
optional, ...)
if (!optional)
names(value) -
Re: [R] POSIXlt converted to POSIXct in as.data.frame()
I'm not qualified to say much about POSIX, but I haven't seen a
reply to this in almost 3 days, so I'll offer a comment in the hopes
that it might be useful or that someone else might correct any
misstatement I might make:
First, I didn't find a discrepancy.
sessionInfo()
R version 2.4.0 (2006-10-03)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
attached base packages:
[1] methods stats graphics grDevices utils datasets
[7] base
I used the following modification extension of your example:
my_POSIXlt - strptime(c(11-09-2006, 11-10-2006, 11-11-2006,
11-12-2006, 11-13-2006), %m-%d-%Y)
str(my_POSIXlt)
class(my_POSIXlt)
my_Date - as.Date(my_POSIXlt)
str(my_Date)
myCharacters - format(my_Date)
class(myCharacters)
my_DF - data.frame(my_POSIXlt)
str(my_DF)
DF_Date - as.Date(my_DF$my_POSIXlt)
str(DF_Date)
DF_Date
all.equal(DF_Date, my_Date)
# TRUE
The data.frame function converts POSIXlt, which is a list, to
POSIXct, which is a numeric vector with attributes:
attributes(my_DF$my_POSIXlt)
$class
[1] POSIXt POSIXct
$tzone
[1]
is.numeric(my_DF$my_POSIXlt)
[1] TRUE
If you are getting a day shift, I would guess that you might have
a different version of some of the software or a difference in your
locale. I just did 'update.packages()' yesterday, so if I'm out of date
on something, I hope someone will help me understand and fix the problem.
Beyond this, have you reviewed the ?POSIXt help file plus Gabor
Grothendieck and Thomas Petzoldt. R help desk: Date and time classes in
R. R News, 4(1):29-32, June 2004 (available from www.r-project.org -
Newsletter)?
Hope this helps.
Spencer Graves
Roger Bivand wrote:
In trying to use as.Date(), I've come across the conversion of POSIXlt to
POSIXct when a POSIXlt variable is included in a data frame:
my_POSIX - strptime(c(11-09-2006, 11-10-2006, 11-11-2006,
11-12-2006, 11-13-2006), %m-%d-%Y)
str(my_POSIX)
my_Date - as.Date(my_POSIX)
str(my_Date)
data - format(my_Date)
str(data)
my_DF - data.frame(my_POSIX)
str(my_DF)
DF_Date - as.Date(my_DF$my_POSIX)
str(DF_Date)
DF_Date
The consequence (for my LC_TIME and machine time zone) is that when
as.Date() is applied to the data frame column, it dispatches on
as.Date.POSIXct() not as.Date.POSIXlt(), causing a day shift (actually 60
minutes, but because as.Date.POSIXct() says floor(), it ends up being a
whole day). Should data.frame() be changing POSIXlt to POSIXct?
As as.data.frame.POSIXlt() is written, it says:
as.data.frame.POSIXlt
function (x, row.names = NULL, optional = FALSE, ...)
{
value - as.data.frame.POSIXct(as.POSIXct(x), row.names,
optional, ...)
if (!optional)
names(value) - deparse(substitute(x))[[1]]
value
}
environment: namespace:base
which seems a little brutal. Using I() seems to be a work-around:
my_DF - data.frame(my_POSIXa=I(my_POSIX))
str(my_DF)
class(my_DF$my_POSIXa)
DF_Date - as.Date(my_DF$my_POSIXa)
str(DF_Date)
DF_Date
In the original problem (conversion of a list read from PostgreSQL to
a data frame with as.data.frame()), having to know that you need to insert
I() is perhaps unexpected.
Roger
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[R] POSIXlt converted to POSIXct in as.data.frame()
In trying to use as.Date(), I've come across the conversion of POSIXlt to
POSIXct when a POSIXlt variable is included in a data frame:
my_POSIX - strptime(c(11-09-2006, 11-10-2006, 11-11-2006,
11-12-2006, 11-13-2006), %m-%d-%Y)
str(my_POSIX)
my_Date - as.Date(my_POSIX)
str(my_Date)
data - format(my_Date)
str(data)
my_DF - data.frame(my_POSIX)
str(my_DF)
DF_Date - as.Date(my_DF$my_POSIX)
str(DF_Date)
DF_Date
The consequence (for my LC_TIME and machine time zone) is that when
as.Date() is applied to the data frame column, it dispatches on
as.Date.POSIXct() not as.Date.POSIXlt(), causing a day shift (actually 60
minutes, but because as.Date.POSIXct() says floor(), it ends up being a
whole day). Should data.frame() be changing POSIXlt to POSIXct?
As as.data.frame.POSIXlt() is written, it says:
as.data.frame.POSIXlt
function (x, row.names = NULL, optional = FALSE, ...)
{
value - as.data.frame.POSIXct(as.POSIXct(x), row.names,
optional, ...)
if (!optional)
names(value) - deparse(substitute(x))[[1]]
value
}
environment: namespace:base
which seems a little brutal. Using I() seems to be a work-around:
my_DF - data.frame(my_POSIXa=I(my_POSIX))
str(my_DF)
class(my_DF$my_POSIXa)
DF_Date - as.Date(my_DF$my_POSIXa)
str(DF_Date)
DF_Date
In the original problem (conversion of a list read from PostgreSQL to
a data frame with as.data.frame()), having to know that you need to insert
I() is perhaps unexpected.
Roger
--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [EMAIL PROTECTED]
__
R-help@stat.math.ethz.ch mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
