[R] How to make a vector/list/array of POSIXlt object?

[Gabor Grothendieck]

If the problem is that you have a vector of dates, a vector of times
and a vector of data and you want to create a data frame with one
POSIXct column and one column of data then try this:

dd <- c("01/22/2008", "02/13/2008")
tt <- c("01:01:00", "23:01:12")
dat <- 1:2

data.frame(dt = strptime(paste(dd, tt), "%m/%d/%Y %H:%M:%S"), dat)

# if you don't need subsecond data or time zones you could use chron

library(chron)
data.frame(dt = chron(dd, tt), dat)

If this is intended to be a time series you might want to look at the zoo
package.  It has three vignettes that give more info.


On Feb 17, 2008 11:54 PM, Bo Zhou <bozhou1981 at hotmail.com> wrote:
> Hi Gabor,
>
> I'm using this code but it doesn't work for me
>
> > strptime2<-function (date,time) as.POSIXct(strptime(paste(date,time),
> "%m/%d/%Y %H:%M:%S"))
> > dt=mapply(strptime2, "01/01/2008", "00:00:00", SIMPLIFY=FALSE,
> USE.NAMES=FALSE)
> > df=data.frame(X1=dt,X2=1)
> > dt
> [[1]]
> [1] "2008-01-01 Eastern Standard Time"
>
> > df
>   structure.1199163600..class...c..POSIXt....POSIXct....tzone...... X2
> 1                                                        2008-01-01  1
>
> Here df looks very wrong to me.
>
> So I tested this code:
>
> > df2=data.frame(X1=as.POSIXct(Sys.time()),X2=1)
> > df2
>                    X1 X2
> 1 2008-02-17 23:43:08  1
> > class(df2$X1)
> [1] "POSIXt"  "POSIXct"
>
> Ah this worked as I expected.
>
> So some tweaking here - SIMPLIFY is set TRUE now:
>
> > strptime2<-function (date,time) as.POSIXct(strptime(paste(date,time),
> "%m/%d/%Y %H:%M:%S"))
> > dt=mapply(strptime2, "01/01/2008", "00:00:00", SIMPLIFY=TRUE,
> USE.NAMES=FALSE)
> > df=data.frame(X1=dt,X2=1)
> > df
>           X1 X2
> 1 1199163600  1
> > class(df$X1)
> [1] "numeric"
>
> Hmm... it worked, but not in a way I wanted. The class info is missing.
>
> So how to get the result like this below? I do need that mapply +
> strptime(paste), cos my CSV file is formatted in that way!
>
> > df2
>                    X1 X2
> 1 2008-02-17 23:43:08  1
> > class(df2$X1)
> [1] "POSIXt"  "POSIXct"
>
>
> Any insight?
>
> Cheers,
>
> Bo
>
>
>
> > Date: Sun, 17 Feb 2008 15:53:28 -0500
> > From: ggrothendieck at gmail.com
> > To: bozhou1981 at hotmail.com
> > Subject: Re: [R] How to make a vector/list/array of POSIXlt object?
> > CC: r-help at r-project.org
>
>
> >
> > Normally one uses POSIXct rather than POSIXlt for storage. See R News 4/1
> for
> > more info on date and time classes.
> >
> > On Feb 17, 2008 3:45 PM, Bo Zhou <bozhou1981 at hotmail.com> wrote:
> > >
> > > Hi Guys,
> > >
> > > I'm cooking up my time series code. I want a data frame with first
> column as timestamp in POSIXlt format.
> > >
> > > I hit on this the problem of how to create an array/list/vector of
> POSIXlt objects. Code is as follows
> > >
> > >
> > >
> > > > dtt=array(dim = 2)
> > > > t=as.POSIXlt( strptime("07/12/07 13:20:01", "%m/%d/%Y
> %H:%M:%S",tz="GMT"))
> > > > dtt
> > > [1] NA NA
> > > > t
> > > [1] "0007-07-12 13:20:01 GMT"
> > > > dtt[1]=t
> > > Warning message:
> > > In dtt[1] = t :
> > > number of items to replace is not a multiple of replacement length
> > > > class(dtt)
> > > [1] "list"
> > > > class(t)
> > > [1] "POSIXt" "POSIXlt"
> > > > unclass(t)
> > > $sec
> > > [1] 1
> > >
> > > $min
> > > [1] 20
> > >
> > > $hour
> > > [1] 13
> > >
> > > $mday
> > > [1] 12
> > >
> > > $mon
> > > [1] 6
> > >
> > > $year
> > > [1] -1893
> > >
> > > $wday
> > > [1] 4
> > >
> > > $yday
> > > [1] 192
> > >
> > > $isdst
> > > [1] 0
> > >
> > > attr(,"tzone")
> > > [1] "GMT"
> > >
> > >
> > >
> > > Seems like POSIXlt is matrix in this case.
> > >
> > > Any suggestions?
> > >
> > > Cheers,
> > >
> > > B
> > > _________________________________________________________________
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