On May 23, 2013, at 7:06 PM, Denis Chabot wrote:
> Thank you for the 2 methods to make the columns class Date, but I would
> really like to know why these variables were not in Date class with my code.
> Do you know?
I suspect that the problem lies in the dispatch to `[<-.<class>` or `$<-`. When
the first argument is 'logical', then the first argument is not of class Date
and so not dispatched to `[<-.Date` but rather to .Primitive("[<-"), there
being no `$<-.logical or `[<-.logical` .
"Arguably", as it were, someone should write S4 methods for `[<-` and `$<-`
that would dispatch to the expected method on a signature where the second
argument is a Date or POSIXct class. We might also then want methods for the
other two "[/$" indexing classes, "numeric" and "character".
--
David.
>
> Denis
>
>
> Le 2013-05-23 à 21:44, arun <smartpink...@yahoo.com> a écrit :
>
>> You could convert those columns to "Date" class by:
>>
>>
>> Data[,c(4,6)]<-lapply(Data[,c(4,6)],as.Date,origin="1970-01-01")
>> #or
>> Data[,c(4,6)]<-lapply(Data[,c(4,6)],function(x) structure(x,class="Date"))
>>
>>
>> # dat1 dat2 Dat1a Dat1b Dat2a Dat2b
>> #1 41327 41327 2013-02-22 2013-02-22 2013-02-22 2013-02-22
>> #2 41334 41334 2013-03-01 2013-03-01 2013-03-01 2013-03-01
>> #3 41341 41341 2013-03-08 2013-03-08 2013-03-08 2013-03-08
>> #4 41348 41348 2013-03-15 2013-03-15 2013-03-15 2013-03-15
>> #5 41355 NA 2013-03-22 2013-03-22 <NA> <NA>
>> #6 41362 41362 2013-03-29 2013-03-29 2013-03-29 2013-03-29
>> #7 41369 41369 2013-04-05 2013-04-05 2013-04-05 2013-04-05
>> #8 41376 41376 2013-04-12 2013-04-12 2013-04-12 2013-04-12
>> #9 41383 NA 2013-04-19 2013-04-19 <NA> <NA>
>> #10 41390 41390 2013-04-26 2013-04-26 2013-04-26 2013-04-26
>> #11 41397 41397 2013-05-03 2013-05-03 2013-05-03 2013-05-03
>> A.K.
>>
>> ----- Original Message -----
>> From: Denis Chabot <chabot.de...@gmail.com>
>> To: R-help@r-project.org
>> Cc:
>> Sent: Thursday, May 23, 2013 5:35 PM
>> Subject: [R] subsetting and Dates
>>
>> Hi,
>>
>> I am trying to understand why creating Date variables does not work if I
>> subset to avoid NAs.
>>
>> I had problems creating these Date variables in my code and I thought that
>> the presence of NAs was the cause. So I used a condition to avoid NAs.
>>
>> It turns out that NAs are not a problem and I do not need to subset, but I'd
>> like to understand why subsetting causes the problem.
>> The strange numbers I start with are what I get when I read an Excel sheet
>> with the function read.xls() from package gdata.
>>
>> dat1 = c(41327, 41334, 41341, 41348, 41355, 41362, 41369, 41376, 41383,
>> 41390, 41397)
>> dat2 = dat1
>> dat2[c(5,9)]=NA
>> Data = data.frame(dat1,dat2)
>>
>> keep1 = !is.na(Data$dat1)
>> keep2 = !is.na(Data$dat2)
>>
>>
>> Data$Dat1a = as.Date(Data[,"dat1"], origin="1899-12-30")
>> Data$Dat1b[keep1] = as.Date(Data[keep1,"dat1"], origin="1899-12-30")
>> Data$Dat2a = as.Date(Data[,"dat2"], origin="1899-12-30")
>> Data$Dat2b[keep2] = as.Date(Data[keep2,"dat2"], origin="1899-12-30")
>>
>> Data
>> dat1 dat2 Dat1a Dat1b Dat2a Dat2b
>> 1 41327 41327 2013-02-22 15758 2013-02-22 15758
>> 2 41334 41334 2013-03-01 15765 2013-03-01 15765
>> 3 41341 41341 2013-03-08 15772 2013-03-08 15772
>> 4 41348 41348 2013-03-15 15779 2013-03-15 15779
>> 5 41355 NA 2013-03-22 15786 <NA> NA
>> 6 41362 41362 2013-03-29 15793 2013-03-29 15793
>> 7 41369 41369 2013-04-05 15800 2013-04-05 15800
>> 8 41376 41376 2013-04-12 15807 2013-04-12 15807
>> 9 41383 NA 2013-04-19 15814 <NA> NA
>> 10 41390 41390 2013-04-26 15821 2013-04-26 15821
>> 11 41397 41397 2013-05-03 15828 2013-05-03 15828
>>
>> So variables Dat1b and Dat2b are not converted to Date class.
>>
>>
>> sessionInfo()
>> R version 2.15.2 (2012-10-26)
>> Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
>>
>> locale:
>> [1] fr_CA.UTF-8/fr_CA.UTF-8/fr_CA.UTF-8/C/fr_CA.UTF-8/fr_CA.UTF-8
>>
>> attached base packages:
>> [1] stats graphics grDevices utils datasets methods base
>>
>> other attached packages:
>> [1] gdata_2.12.0
>>
>> loaded via a namespace (and not attached):
>> [1] gtools_2.7.0
>>
>> Thanks in advance,
>>
>> Denis
David Winsemius
Alameda, CA, USA
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