On Mar 9, 2013, at 9:24 AM, Alexandre Sieira wrote:
> I understand that the two following loops should produce the exact same
> output. However, they do not. It appears that looping directly through the
> sequence of Date objects somehow makes them be coerced to numeric:
>
>> date1 = "20130301"
>> date2 = "20130302"
>>
>> d1 = as.Date(date1, format="%Y%m%d", tz="GMT")
>> d2 = as.Date(date2, format="%Y%m%d", tz="GMT")
>>
>> range = seq(from=d1, to=d2, by="day")
>> for (i in 1:length(range)) print(class(range[i]))
>
> [1] "Date"
> [1] "Date"
>>
>> for (i in seq(from=d1, to=d2, by="day")) print(class(i))
> [1] "numeric"
> [1] "numeric"
>
> This is output from R version 2.15.2 (2012-10-26) on Mac OS X 10.8.2.
>
> Is this expected behavior?
It wasn't expected by me either, but it is what both my Mac R 2.15.3 and my
Windows(32bit) 2.15.1 display. If you put those dates in a list, you do not get
the coercion:
> for (i in list(d1,d2)) print(class(i))
[1] "Date"
[1] "Date"
I was unable to find the reason for the original coercion in the help("for")
page or the R Language Definition entry regarding for-loops. On the hunch that
coercion via as.vector might be occurring, I tried with with a factor vector
and did see that it was coerced to "character" which is the behavior that would
be expected if that were happening behind the scenes:
ff <- factor(letters[1:3])
as.vector(ff)
#[1] "a" "b" "c"
for (i in ff) print(class(i))
#[1] "character"
#[1] "character"
#[1] "character"
(I also tried searching for loop in the R Internals document and found nothing
that explained this to me.)
--
David.
> --
> Alexandre Sieira
> CISA, CISSP, ISO 27001 Lead Auditor
>
> "The truth is rarely pure and never simple."
> Oscar Wilde, The Importance of Being Earnest, 1895, Act I
>
>
> Sent with Sparrow (http://www.sparrowmailapp.com/?sig)
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
