R help - Jan 2007 - Simple Date problems with cbind

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)

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"

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

> It is probably something blindingly simple but can
> anyone suggest something?
You need to use the format code "%Y" for 4-digits years.
You need to create a data frame using 'data.frame()' (cbind() creates a 
matrix when given just vectors).

 > as.Date(c("2005/01/24" ,"2006/01/23"
,"2006/01/23"), "%Y/%m/%d")
[1] "2005-01-24" "2006-01-23" "2006-01-23"
 > data.frame(int=1:3, date=as.Date(c("2005/01/24"
,"2006/01/23"
,"2006/01/23"), "%Y/%m/%d"))
   int       date
1   1 2005-01-24
2   2 2006-01-23
3   3 2006-01-23
 > (x <- data.frame(int=1:3, date=as.Date(c("2005/01/24"
,"2006/01/23"
,"2006/01/23"), "%Y/%m/%d")))
   int       date
1   1 2005-01-24
2   2 2006-01-23
3   3 2006-01-23
 > class(x)
[1] "data.frame"
 > sapply(x, class)
       int      date
"integer"    "Date"
 >

-- Tony Plate

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