[R] subsetting and Dates

[Denis Chabot]

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
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