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POSIXlt and trunc

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James Long-2

POSIXlt and trunc

Hi,

I'm having trouble understanding how trunc is operating on vectors of
POSIXlt objects. Why does dates[1:4] in the last line return a bunch of NAs
even though dates look like it has all the right elements? This worries me
that something is off with my use of trunc. Is trunc not suppose to be
vectorized with POSIXlt? If not, then how should I truncate a bunch of
POSIXlt objects? I'm using R 2.11.1 with linux. (easy cut and paste R code
below)

> dates <- c("2011-12-30 20:03:18 PST","2012-01-08 19:10:00 PST",
+ "2012-01-15 22:00:10 PST","2012-01-26 20:01:00 PST",
+ "2012-01-27 21:25:01 PST","2012-01-19 20:17:31 PST",
+ "2012-01-31 21:01:00 PST","2012-01-15 21:01:00 PST",
+ "2012-01-04 21:03:00 PST","2012-01-04 20:00:00 PST")
> dates = as.POSIXlt(dates)
> dates[1:4]
[1] "2011-12-30 20:03:18" "2012-01-08 19:10:00" "2012-01-15 22:00:10"
[4] "2012-01-26 20:01:00"
> class(dates)
[1] "POSIXt" "POSIXlt"
> ### this all looks normal so far, now for truncating
> dates = trunc(dates,units="hours")
> class(dates)
[1] "POSIXt" "POSIXlt"
> dates
[1] "2011-12-30 20:00:00" "2012-01-08 19:00:00" "2012-01-15 22:00:00"
[4] "2012-01-26 20:00:00" "2012-01-27 21:00:00" "2012-01-19 20:00:00"
[7] "2012-01-31 21:00:00" "2012-01-15 21:00:00" "2012-01-04 21:00:00"
[10] "2012-01-04 20:00:00"
> dates[1:4]
[1] "2011-12-30 20:00:00" NA NA
[4] NA
> # what?

Easy cut and paste code:

dates <- c("2011-12-30 20:03:18 PST","2012-01-08 19:10:00 PST",
"2012-01-15 22:00:10 PST","2012-01-26 20:01:00 PST",
"2012-01-27 21:25:01 PST","2012-01-19 20:17:31 PST",
"2012-01-31 21:01:00 PST","2012-01-15 21:01:00 PST",
"2012-01-04 21:03:00 PST","2012-01-04 20:00:00 PST")
dates = as.POSIXlt(dates)
dates[1:4]
class(dates)
dates = trunc(dates,units="hours")
class(dates)
dates
dates[1:4]

Thanks for your help!
James

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Rui Barradas

Re: POSIXlt and trunc

Hello,

It works with me. Problem with R version? OS?

sessionInfo()
R version 2.15.0 (2012-03-30)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=Portuguese_Portugal.1252
LC_CTYPE=Portuguese_Portugal.1252
[3] LC_MONETARY=Portuguese_Portugal.1252 LC_NUMERIC=C

[5] LC_TIME=Portuguese_Portugal.1252

attached base packages:
[1] stats graphics grDevices utils datasets methods base

loaded via a namespace (and not attached):
[1] tools_2.15.0

Hope this helps,

Rui Barradas

Em 15-06-2012 06:06, James Long escreveu:

> Hi,
>
> I'm having trouble understanding how trunc is operating on vectors of
> POSIXlt objects. Why does dates[1:4] in the last line return a bunch of NAs
> even though dates look like it has all the right elements? This worries me
> that something is off with my use of trunc. Is trunc not suppose to be
> vectorized with POSIXlt? If not, then how should I truncate a bunch of
> POSIXlt objects? I'm using R 2.11.1 with linux. (easy cut and paste R code
> below)
>
>
>> dates <- c("2011-12-30 20:03:18 PST","2012-01-08 19:10:00 PST",
> + "2012-01-15 22:00:10 PST","2012-01-26 20:01:00 PST",
> + "2012-01-27 21:25:01 PST","2012-01-19 20:17:31 PST",
> + "2012-01-31 21:01:00 PST","2012-01-15 21:01:00 PST",
> + "2012-01-04 21:03:00 PST","2012-01-04 20:00:00 PST")
>> dates = as.POSIXlt(dates)
>> dates[1:4]
> [1] "2011-12-30 20:03:18" "2012-01-08 19:10:00" "2012-01-15 22:00:10"
> [4] "2012-01-26 20:01:00"
>> class(dates)
> [1] "POSIXt" "POSIXlt"
>> ### this all looks normal so far, now for truncating
>> dates = trunc(dates,units="hours")
>> class(dates)
> [1] "POSIXt" "POSIXlt"
>> dates
> [1] "2011-12-30 20:00:00" "2012-01-08 19:00:00" "2012-01-15 22:00:00"
> [4] "2012-01-26 20:00:00" "2012-01-27 21:00:00" "2012-01-19 20:00:00"
> [7] "2012-01-31 21:00:00" "2012-01-15 21:00:00" "2012-01-04 21:00:00"
> [10] "2012-01-04 20:00:00"
>> dates[1:4]
> [1] "2011-12-30 20:00:00" NA NA
> [4] NA
>> # what?
>
>
> Easy cut and paste code:
>
> dates <- c("2011-12-30 20:03:18 PST","2012-01-08 19:10:00 PST",
> "2012-01-15 22:00:10 PST","2012-01-26 20:01:00 PST",
> "2012-01-27 21:25:01 PST","2012-01-19 20:17:31 PST",
> "2012-01-31 21:01:00 PST","2012-01-15 21:01:00 PST",
> "2012-01-04 21:03:00 PST","2012-01-04 20:00:00 PST")
> dates = as.POSIXlt(dates)
> dates[1:4]
> class(dates)
> dates = trunc(dates,units="hours")
> class(dates)
> dates
> dates[1:4]
>
>
> Thanks for your help!
> James
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] mailing list
> 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.
>

______________________________________________
[hidden email] mailing list
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.

Michael Weylandt

Re: POSIXlt and trunc

In reply to this post by James Long-2

General rule of thumb: use POSIXct rather than POSIXlt for such things
and only convert to POSIXlt (losslessly) at the end of your
calculations when you need it for display reasons. Internally, POSIXct
is just a double, so it is nice to do calculations on, while POSIXlt
is a list-like object which tries to handle the book-keeping of all
sorts of different time elements. See RNews 4/1 for more detail.

Not sure if this is immediately the problem at hand, but I've found it
to be good practice.

Best,
Michael

On Fri, Jun 15, 2012 at 12:06 AM, James Long <[hidden email]> wrote: