[R] Simple Date problems with cbind

[Marc Schwartz]

On Tue, 2007-01-30 at 15:27 -0500, John Kane wrote:
> I am clearly misunderstanding something about dates
> and my reading of the help and RSiteSearch have not
> turned up anything. 
> 
> I have a variable of class "Date" and I want to add
> include it in a data.frame. However when do a cbind
> the date var is coerced into a numeric. 
> 
> However when I tried to create a example I also seem
> to be doing something wrong as I cannot seem even  to
> create a date class var even when I try to copy an
> example from the Help
> 
> Example from Help
> dates <- c("02/27/92", "02/27/92", "01/14/92",
> "02/28/92", "02/01/92")
> max <-as.Date(dates, "%m/%d/%y")
> max
> class(max)
> 
> Results
> > dates <- c("02/27/92", "02/27/92", "01/14/92",
> "02/28/92", "02/01/92")
> > max <-as.Date(dates, "%m/%d/%y")
> > max
> [1] "1992-02-27" "1992-02-27" "1992-01-14"
> "1992-02-28" "1992-02-01"
> > class(max)
> [1] "Date"
> 
> 
> My example
> 
> cc <- c("2005/01/24" ,"2006/01/23" ,"2006/01/23",
> "2006/01/23")
> xx <- as.Date(cc, "%y/%m/%d")
> xx
> class(xx)


You need to use a capital "Y" for a four digit year...

See ?strftime for more information on date formats.


> Results
> > cc <- c("2005/01/24" ,"2006/01/23" ,"2006/01/23",
> "2006/01/23")
> > xx <- as.Date(cc, "%y/%m/%d")
> > xx
> [1] NA NA NA NA
> > class(xx)
> [1] "Date"


> cc <- c("2005/01/24" ,"2006/01/23" ,"2006/01/23",
          "2006/01/23")

xx <- as.Date(cc, "%Y/%m/%d")

> xx
[1] "2005-01-24" "2006-01-23" "2006-01-23" "2006-01-23"

> class(xx)
[1] "Date"



> And on to the cbind problem
> 
> jj <- 1:5
> cbind(jj,max)
> 
>    jj  max
> [1,]  1 8092
> [2,]  2 8092
> [3,]  3 8048
> [4,]  4 8093
> [5,]  5 8066
> 
> I have tried various as.Date etc approcaes
> 
> It is probably something blindingly simple but can
> anyone suggest something?
> 
> Thanks

In this case, you are trying to cbind() a numeric vector and a Date
vector into a matrix.  Since a matrix may only have one data type, the
Date vector will be coerced to numeric.

If you want mixed data types, you need to create a data frame:

jj <- 1:4
DF <- data.frame(jj, xx)

> DF
  jj         xx
1  1 2005-01-24
2  2 2006-01-23
3  3 2006-01-23
4  4 2006-01-23

> str(DF)
'data.frame':   4 obs. of  2 variables:
 $ jj: int  1 2 3 4
 $ xx:Class 'Date'  num [1:4] 12807 13171 13171 13171


Alternatively, create an initial data frame with 'jj' and then cbind()
'xx':

JJ <- data.frame(jj)

> str(JJ)
'data.frame':   4 obs. of  1 variable:
 $ jj: int  1 2 3 4

DF <- cbind(JJ, xx)

> str(DF)
'data.frame':   4 obs. of  2 variables:
 $ jj: int  1 2 3 4
 $ xx:Class 'Date'  num [1:4] 12807 13171 13171 13171


Once you create the initial data frame, cbind() will then use the
appropriate approach based upon the first argument already being a data
frame.

HTH,

Marc Schwartz