[R] character to time problem

[John Kane]

--- Jason Barnhart <jasoncbarnhart at msn.com> wrote:

> Hi John,
> 
> a) The NA appears because '30/02/1995' is not a
> valid date.
> 
>     > strptime('30/02/1995' , "%d/%m/%Y")
>     [1] NA
>

I knew we should never have moved to the Gregorian
Calender!  

Thanks.  I accidently made up the date but this means
that I have some invalid dates in the file. Not a
problem now I know what's happening. And our contract
says someone else gets to fix them :)

> b) dates which has the following classes uses
> sort.POSIXlt which in 
> turns sets na.last to NA.  ?order details how NA's
> are handled in 
> ordering data via na.last.
> 
>     > class(dates)
>     [1] "POSIXt"  "POSIXlt"
> 
>     > methods(sort)
>     [1] sort.default sort.POSIXlt
> 
>     > sort.POSIXlt
>     function (x, decreasing = FALSE, na.last = NA,
> ...)
>     x[order(as.POSIXct(x), na.last = na.last,
> decreasing = 
> decreasing)]
>     <environment: namespace:base>
> 
> After resetting the Feb. date the code works.
> 
> HTH,
> -jason
> 

So it does.  

I had not thought to look at the sort.POSIXlt
function.  I don't quite understand what na.last is
doing and don't seem to see the documentation.  Is it
sorting the NA's to the last place(s) in the vector
and then dropping them? 

Thanks again

> ----- Original Message ----- 
> From: "John Kane" <jrkrideau at yahoo.ca>
> To: "R R-help" <r-help at stat.math.ethz.ch>
> Sent: Thursday, June 07, 2007 2:17 PM
> Subject: [R] character to time problem
> 
> 
> >I am trying to clean up some dates and I am clearly
> > doing something wrong.  I have laid out an example
> > that seems to show what is happening with the
> "real"
> > data.  The  coding is lousy but it looks like it
> > should have worked.
> >
> > Can anyone suggest a) why I am getting that NA
> > appearing after the strptime() command and b) why
> the
> > NA is disappearing in the sort()? It happens with
> > na.rm=TRUE  and na.rm=FALSE
> > -------------------------------------------------
> > aa  <- data.frame( c("12/05/2001", " ",
> "30/02/1995",
> > NA, "14/02/2007", "M" ) )
> > names(aa)  <- "times"
> > aa[is.na(aa)] <- "M"
> > aa[aa==" "]  <- "M"
> > bb <- unlist(subset(aa, aa[,1] !="M"))
> > dates <- strptime(bb, "%d/%m/%Y")
> > dates
> > sort(dates)
> > --------------------------------------------------
> >
> > Session Info
> > R version 2.4.1 (2006-12-18)
> > i386-pc-mingw32
> >
> > locale:
> > LC_COLLATE=English_Canada.1252;
> > LC_CTYPE=English_Canada.1252;
> > LC_MONETARY=English_Canada.1252;
> > LC_NUMERIC=C;LC_TIME=English_Canada.1252
> >
> > attached base packages:
> > [1] "stats"     "graphics"  "grDevices" "utils"
> > "datasets"  "methods"   "base"
> >
> > other attached packages:
> >  gdata   Hmisc
> > "2.3.1" "3.3-2"
> >
> > (Yes I know I'm out of date but I don't like
> > upgrading just as I am finishing a project)
> >
> > Thanks
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch 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.
> > 
> 
>