[R] subsetting and Dates

Fri May 24 07:33:57 CEST 2013

On May 23, 2013, at 7:56 PM, arun wrote:

> I guess it is due to vectorization.

The concept of "vectorization" is much broader than the activities of `as.vector`, but it needs a specific functional mechanism to be considered an explanation.

> vec1<- as.Date(Data[,2],origin="1899-12-30")
> class(vec1)
> #[1] "Date"
>  as.vector(vec1)
> # [1] 15758 15765 15772 15779    NA 15793 15800 15807    NA 15821 15828

It is certainly true that `as.vector` could unclass a Date-classed vector, but why do you believe this has anything to do with how `$<-` returns its functional result? Setting `trace` on `as.vector` does not result in any signal suggesting that it was called:

> trace('as.vector')
> Data$Dat1b = as.Date(Data[ ,"dat1"], origin="1899-12-30")

# Nothing

> trace( .Primitive("$<-") )
> Data$Dat1b = as.Date(Data[ ,"dat1"], origin="1899-12-30")
trace: `$<-`(`*tmp*`, Dat1b, value = c(15758, 15765, 15772, 15779, 15786, 
15793, 15800, 15807, 15814, 15821, 15828))

> 
>  head(as.list(vec1),2)
> #[[1]]
> #[1] "2013-02-22"
> #
> #[[2]]
> #[1] "2013-03-01"
>  head(data.frame(vec1),2)
> #        vec1
> #1 2013-02-22
> #2 2013-03-01
> 
> 
> unlist(as.list(vec1))
> # [1] 15758 15765 15772 15779    NA 15793 15800 15807    NA 15821 15828
>  
> 
> Also, please check:
> 
> http://r.789695.n4.nabble.com/as-vector-with-mode-quot-list-quot-and-POSIXct-td4667533.html

Interesting but I fail to see the connection to this instance other than R behaving somewhat differently than we might at one time have expected.

-- 
David.

> 
> A.K.
> 
> ----- Original Message -----
> From: Denis Chabot <chabot.denis at gmail.com>
> To: arun <smartpink111 at yahoo.com>
> Cc: R help <r-help at r-project.org>
> Sent: Thursday, May 23, 2013 10:06 PM
> Subject: Re: [R] subsetting and Dates
> 
> 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?
> 
> Denis
> 
> 
> Le 2013-05-23 à 21:44, arun <smartpink111 at 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.denis at gmail.com>
>> To: R-help at 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
>> ______________________________________________
>> R-help at 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.
>> 
> 
> 
> ______________________________________________
> R-help at 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