[R] character to time problem

[Jason Barnhart]

Hi John,

a) The NA appears because '30/02/1995' is not a valid date.

    > strptime('30/02/1995' , "%d/%m/%Y")
    [1] NA

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

----- 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 (Yes I know I'm out of date but I don't like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
>
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