strftime fails on POSIXct objects (PR#10695)

donaldcallen at gmail.com wrote:
R 2.6.1 on a Thinkpad T60 running up-to-date Gentoo:

Despite the documentation, which says:

     'strftime' is an alias for 'format.POSIXlt', and 'format.POSIXct'
     first converts to class '"POSIXlt"' by calling 'as.POSIXlt'.  Note
     that only that conversion depends on the time zone.

strftime fails on POSIXct objects:

I think the author of those lines would point out that they do NOT imply
that it shouldn't fail.... In fact, why would you expect
format.POSIXlt(x) to work on anything but POSIXlt objects?
Ah, you are quite right -- I mis-read the documentation.

Thanks --
/Don Allen
    -p

foo <- as.POSIXct(strptime(x='2007-09-22', format='%Y-%m-%d'))
strftime(x=foo, format='%Y-%m-%d')

Error in strftime(x = foo, format = "%Y-%m-%d") : wrong class

It's pretty clear why, given the first two lines of the function:

strftime

function (x, format = "", usetz = FALSE, ...)
{
    if (!inherits(x, "POSIXlt"))
        stop("wrong class")
    if (format == "") {
        times <- unlist(unclass(x)[1:3])
        secs <- x$sec
        secs <- secs[!is.na(secs)]
        np <- getOption("digits.secs")
        if (is.null(np))
            np <- 0
        else np <- min(6, np)
        if (np >= 1) {
            for (i in (1:np) - 1) if (all(abs(secs - round(secs,
                i)) < 1e-06)) {
                np <- i
                break
            }
        }
        format <- if (all(times[!is.na(times)] == 0))
            "%Y-%m-%d"
        else if (np == 0)
            "%Y-%m-%d %H:%M:%S"
        else paste("%Y-%m-%d %H:%M:%OS", np, sep = "")
    }
    .Internal(format.POSIXlt(x, format, usetz))
}
<environment: namespace:base>

/Don Allen

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strftime fails on POSIXct objects (PR#10695)

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