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:
> 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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