[R] Coercing a dataframe column to datetime

[richard.kittler@amd.com]

Sorry to bother you all with this one. I determined that the problem is solved if I use 'lapply' rather than 'sapply'.  Since sapply returns the result as a vector it must be making a best guess of numeric for the class of the result (?)

--Rich

Richard Kittler 
AMD TDG
408-749-4099

-----Original Message-----
From: Kittler, Richard 
Sent: Tuesday, June 15, 2004 11:32 AM
To: 'Prof Brian Ripley'
Cc: r-help at stat.math.ethz.ch
Subject: RE: [R] Coercing a dataframe column to datetime


Thank you! The next step in the conversion still fails and I can't seem to find any examples in the archives.  The result of the function 'as.POSIXct(strptime())' within the 'sapply' comes back as numeric rather than POSIXct as expected: 

> ds <- cbind(1:2, c("02/27/92 23:03:20", "02/27/92 22:29:56")); ds
     [,1] [,2]               
[1,] "1"  "02/27/92 23:03:20"
[2,] "2"  "02/27/92 22:29:56"
> q <- sapply(ds[,2], function(x) as.POSIXct(strptime(x,"%m/%d/%y 
> %H:%M:%S")))
> class(q) 
[1] "numeric"
> q
02/27/92 23:03:20 02/27/92 22:29:56 
        699260600         699258596 

--Rich

Richard Kittler 
AMD TDG
408-749-4099

-----Original Message-----
From: Prof Brian Ripley [mailto:ripley at stats.ox.ac.uk] 
Sent: Monday, June 14, 2004 12:05 PM
To: Kittler, Richard
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] Coercing a dataframe column to datetime


You have forgotten as.POSIXct is needed too.

On Mon, 14 Jun 2004 richard.kittler at amd.com wrote:

> I am trying to coerce a data frame column from character to datetime using strptime but keep getting an error because the length of the coerced object is always 9.  What am I doing wrong here:   
> 
> .................................................................
> > ds <- cbind(1:2, c("02/27/92 23:03:20", "02/27/92 22:29:56")); ds
>      [,1] [,2]               
> [1,] "1"  "02/27/92 23:03:20"
> [2,] "2"  "02/27/92 22:29:56"
> >  
> > q <- strptime(ds[,2], "%m/%d/%y %H:%M:%S"); q
> [1] "1992-02-27 23:03:20" "1992-02-27 22:29:56"
> > 
> > ds[,2] <- q
> Error in "[<-"(`*tmp*`, , 2, value = q) : number of items to replace
> is not a multiple of replacement length
> > 
> > length(q)
> [1] 9
> 
> .................................................................
> 
> --Rich
> 
> Richard Kittler
> AMD TDG
> 408-749-4099
> 
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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Oxford OX1 3TG, UK                Fax:  +44 1865 272595