R devel - Apr 2006 - as.factor: changed behaviour for Date class

Dear all,
I have noticed a little change in the behaviour of as.factor from R-2.2.1 to
R-2.3.0, and can't find it in the NEWS.

In R-2.3.0:
> times <- 1:5
> class(times) <- "Date"
> as.factor(times)
[1] 1 2 3 4 5
Levels: 1 2 3 4 5

In R-2.2.1:
> as.factor(times)
[1] 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
Levels: 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06

Is this the intended behaviour?
Note that the change is reflected on other functions which seems to use
as.factor internally, for example 'tapply'.
Consider the following code:

times <- 1:5
class(times) <- "Date"
id <- rep(times, each=2)
vals <- rep(1:2,5)
tapply(vals, id, mean)

Under R-2.2.1 this gives:
1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
       1.5        1.5        1.5        1.5        1.5

But under R-2.3.0 the output is:
 1   2   3   4   5
1.5 1.5 1.5 1.5 1.5

Antonio, Fabio Di Narzo.

	[[alternative HTML version deleted]]

The change is not in as.factor: it is in sort (as called by factor) and it 
is documented in the NEWS file.

Why do you expect as.factor to convert a Date object to character and then 
to factor?  Please do the conversion explicitly.

On Thu, 27 Apr 2006, Antonio, Fabio Di Narzo wrote:
> Dear all,
> I have noticed a little change in the behaviour of as.factor from R-2.2.1
to
> R-2.3.0, and can't find it in the NEWS.
>
> In R-2.3.0:
>> times <- 1:5
>> class(times) <- "Date"
>> as.factor(times)
> [1] 1 2 3 4 5
> Levels: 1 2 3 4 5
>
> In R-2.2.1:
>> as.factor(times)
> [1] 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
> Levels: 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
>
> Is this the intended behaviour?
> Note that the change is reflected on other functions which seems to use
> as.factor internally, for example 'tapply'.
> Consider the following code:
>
> times <- 1:5
> class(times) <- "Date"
> id <- rep(times, each=2)
> vals <- rep(1:2,5)
> tapply(vals, id, mean)
>
> Under R-2.2.1 this gives:
> 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
>       1.5        1.5        1.5        1.5        1.5
>
> But under R-2.3.0 the output is:
> 1   2   3   4   5
> 1.5 1.5 1.5 1.5 1.5
>
> Antonio, Fabio Di Narzo.
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
>
-- 
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)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Have you received a reply to this post?  I haven't seen one.
 > t9 <- 9:10
 > class(t9) <- "Date"
 > t9
[1] "1970-01-10" "1970-01-11"
 > as.factor(t9)
[1] 9  10
Levels: 9 10

	  I confirmed what you got with a slightly different example:

 > t9 <- 9:10
 > class(t9) <- "Date"
 > t9
[1] "1970-01-10" "1970-01-11"
# Apparently, 'class(times) <- "Date"' had the anticipated
effect

	  As you indicated, 'as.factor' in R-2.2.1 used character string 
representations of the dates as levels, while in R-2.3.0 it did not:

 > as.factor(t9) # in R-2.3.0
[1] 9  10
Levels: 9 10

 > as.factor(t9) # in R-2.2.1
[1] 1970-01-10 1970-01-11
Levels: 1970-01-10 1970-01-11

	  R-2.2.1 and R-2.3.0 returned the same for the following:
 >  as.numeric(as.factor(t9))
[1] 1 2

 > sessionInfo()
Version 2.3.0 (2006-04-24)
i386-pc-mingw32

attached base packages:
[1] "grid"      "methods"   "stats"    
"graphics"  "grDevices" "utils"
[7] "datasets"  "base"

other attached packages:
  tseries      zoo quadprog  lattice
"0.10-0"  "1.0-6"  "1.4-8" "0.13-8"

 > sessionInfo()
Version 2.3.0 (2006-04-24)
i386-pc-mingw32

attached base packages:
[1] "grid"      "methods"   "stats"    
"graphics"  "grDevices" "utils"
[7] "datasets"  "base"

other attached packages:
  tseries      zoo quadprog  lattice
"0.10-0"  "1.0-6"  "1.4-8" "0.13-8"

	  hope this helps.
	  spencer graves

Antonio, Fabio Di Narzo wrote:
> Dear all,
> I have noticed a little change in the behaviour of as.factor from R-2.2.1
to
> R-2.3.0, and can't find it in the NEWS.
> 
> In R-2.3.0:
> 
>>times <- 1:5
>>class(times) <- "Date"
>>as.factor(times)
> 
> [1] 1 2 3 4 5
> Levels: 1 2 3 4 5
> 
> In R-2.2.1:
> 
>>as.factor(times)
> 
> [1] 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
> Levels: 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
> 
> Is this the intended behaviour?
> Note that the change is reflected on other functions which seems to use
> as.factor internally, for example 'tapply'.
> Consider the following code:
> 
> times <- 1:5
> class(times) <- "Date"
> id <- rep(times, each=2)
> vals <- rep(1:2,5)
> tapply(vals, id, mean)
> 
> Under R-2.2.1 this gives:
> 1970-01-02 1970-01-03 1970-01-04 1970-01-05 1970-01-06
>        1.5        1.5        1.5        1.5        1.5
> 
> But under R-2.3.0 the output is:
>  1   2   3   4   5
> 1.5 1.5 1.5 1.5 1.5
> 
> Antonio, Fabio Di Narzo.
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel