[R] POSIX problem

[Christoph Buser]

Dear David

I tried to reproduce your example. It is not exact the same. When I create
a dataframe, character are transformed to factors except I use I() to
protect "them".

> PeopleData.df <- data.frame(StartDate = c("29/10/2001", "7/12/2001",
                                "16/11/2001", "28/11/2001", "2/11/2001",
                                "26/11/2001"),
                              StartTime = c("15:26", "10:32", "13:58", "14:00",
                                "15:22", "11:15"))
> str(PeopleData.df)
data.frame':	6 obs. of  2 variables:
 $ StartDate: Factor w/ 6 levels "16/11/2001","2/..",..: 5 6 1 4 2 3
 $ StartTime: Factor w/ 6 levels "10:32","11:15",..: 6 1 3 4 5 2

So there is a small difference to your dataframe. Then the following
produces what you want

> as.POSIXct(strptime(paste(PeopleData.df$StartDate,PeopleData.df$StartTime),
                      format="%d/%m/%Y %H:%M"))
[1] "2001-10-29 15:26:00 CET" "2001-12-07 10:32:00 CET"
[3] "2001-11-16 13:58:00 CET" "2001-11-28 14:00:00 CET"
[5] "2001-11-02 15:22:00 CET" "2001-11-26 11:15:00 CET"

Regards,

Christoph

--------------------------------------------------------------
Christoph Buser <buser at stat.math.ethz.ch>
Seminar fuer Statistik, LEO C13
ETH (Federal Inst. Technology)	8092 Zurich	 SWITZERLAND
phone: x-41-44-632-4673		fax: 632-1228
http://stat.ethz.ch/~buser/
--------------------------------------------------------------



David Scott writes:
 > 
 > I am having trouble with creating a POSIXct object. If I create a variable 
 > of class Date first out of the date part of my data, I am ok, but if I 
 > just paste the date and time parts together and try and create the POSIXct 
 > object, I have problems.
 > 
 > Here is a toy example created from the actual data which caused the 
 > problem. I am using R 2.0.1 on Windows XP.
 > 
 > > # Data frame with dates and times, as character
 > > PeopleData.df
 >     StartDate StartTime
 > 1 29/10/2001     15:26
 > 2  7/12/2001     10:32
 > 3 16/11/2001     13:58
 > 4 28/11/2001     14:00
 > 5  2/11/2001     15:22
 > 6 26/11/2001     11:15
 > > str(PeopleData.df)
 > `data.frame':   6 obs. of  2 variables:
 >   $ StartDate: chr  "29/10/2001" "7/12/2001" "16/11/2001" "28/11/2001" ...
 >   $ StartTime: chr  "15:26" "10:32" "13:58" "14:00" ...
 > > dput(PeopleData.df)
 > structure(list(StartDate = c("29/10/2001", "7/12/2001", "16/11/2001",
 > "28/11/2001", "2/11/2001", "26/11/2001"), StartTime = c("15:26",
 > "10:32", "13:58", "14:00", "15:22", "11:15")), .Names = c("StartDate",
 > "StartTime"), row.names = c("1", "2", "3", "4", "5", "6"), class = 
 > "data.frame")
 > > BeginDate <- as.Date(PeopleData.df$StartDate,format="%d/%m/%Y")
 > > BeginDate
 > [1] "2001-10-29" "2001-12-07" "2001-11-16" "2001-11-28" "2001-11-02"
 > [6] "2001-11-26"
 > > # Create POSIXct date-time object without difficulty
 > > BeginTime <- as.POSIXct(format(paste(BeginDate,PeopleData.df$StartTime),
 > +                                 format="%Y/%m/%d %H:%M"))
 > > BeginTime
 > [1] "2001-10-29 15:26:00 New Zealand Standard Time"
 > [2] "2001-12-07 10:32:00 New Zealand Standard Time"
 > [3] "2001-11-16 13:58:00 New Zealand Standard Time"
 > [4] "2001-11-28 14:00:00 New Zealand Standard Time"
 > [5] "2001-11-02 15:22:00 New Zealand Standard Time"
 > [6] "2001-11-26 11:15:00 New Zealand Standard Time"
 > > # But not directly from the dates and times
 > > BeginTime <- 
 > as.POSIXct(format(paste(PeopleData.df$StartDate,PeopleData.df$StartTime),
 > +                                 format="%d/%m/%Y %H:%M"))
 > > BeginTime
 > [1] "0029-10-20 New Zealand Standard Time"
 > [2] "0007-12-20 New Zealand Standard Time"
 > [3] "0016-11-20 New Zealand Standard Time"
 > [4] "0028-11-20 New Zealand Standard Time"
 > [5] "0002-11-20 New Zealand Standard Time"
 > [6] "0026-11-20 New Zealand Standard Time"
 > > # Format looks correct to me
 > > paste(PeopleData.df$StartDate,PeopleData.df$StartTime)
 > [1] "29/10/2001 15:26" "7/12/2001 10:32"  "16/11/2001 13:58" "28/11/2001 
 > 14:00"
 > [5] "2/11/2001 15:22"  "26/11/2001 11:15"
 > 
 > What I think might be causing the problem is the lack of a leading zero 
 > for some of the days (as in 7/12/2001). This doesn't phase as.Date though.
 > 
 > David Scott
 > 
 > 
 > 
 > _________________________________________________________________
 > David Scott	Department of Statistics, Tamaki Campus
 >  		The University of Auckland, PB 92019
 >  		Auckland	NEW ZEALAND
 > Phone: +64 9 373 7599 ext 86830		Fax: +64 9 373 7000
 > Email:	d.scott at auckland.ac.nz
 > 
 > 
 > Graduate Officer, Department of Statistics
 > 
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