I have a reproducible example of my problem below
On Mon, Mar 26, 2012 at 9:22 AM, Joshua Ulrich <josh.m.ulr...@gmail.com>wrote:
> > Given two identical string representations of POSIXct objects, can the
> two
> > objects represent different times?
> >
> Yes. Here's an example (from my Ubuntu machine) of one way:
>
> > (t1 <- Sys.time()); (t2 <- Sys.time())+0.001; t1 == t2
> [1] "2012-03-25 15:13:48 CDT"
> [1] "2012-03-25 15:13:48 CDT"
> [1] FALSE
> > options(digits.secs=3)
> > (t1 <- Sys.time()); (t2 <- Sys.time())+0.001; t1 == t2
> [1] "2012-03-25 15:17:36.520 CDT"
> [1] "2012-03-25 15:17:36.523 CDT"
> [1] FALSE
>
> That is interesting. Of course POSIXct includes more than seconds. The
ones I have been using are rounded to seconds (I assume) so I forgot.
SO I have made the effort and I think I have an example here that
illustrates my problem.
I am hoping there is an equally simple explanation, some little thing I
have missed!
## First I build a little two row XTS in A()
A <- function() {
M <- matrix(ncol=2, byrow=TRUE, c(
"Tue Jan 10 00:00:02 2012",
"0.7843",
"Tue Jan 10 00:00:40 2012",
"0.7842"))
L <- data.frame(M, stringsAsFactors=FALSE)
L[,2] <- as.numeric(L[,2])
L.x <- xts(L[,2], as.POSIXct(L[,1],
format="%a %b %d %T %Y"))
# L.x <- make.index.unique(L.x, drop=TRUE)
names(L.x) <- c( "Value")
return(L.x)
}
## This is a function that is called by sapply that returns the last index
value from the XTS.
f <- function(i, DATA){
TT <- end(DATA)
cat(PAIR, as.character(TT), TT, "\n")
ret <- TT
return(ret)
}
## Put it together...
A.x <- A()
T <- sapply(c(1), f, A.x)
> T <- sapply(c(1), f, A.x)
EUR.CHF 2012-01-10 00:00:40 1326106840
## Note the date displayed as text and in "seconds since epoch" format.
That was emitted by f() using cat()
## T is returned as numeric so needs to be converted to to a time to index
A.x
P <- as.POSIXct(T, origin="1970-01-01")
## P should be the index to the last value of A.x
cat(as.character(P), "\n")
> cat(as.character(P), "\n")
2012-01-09 12:00:40
>
## It is 12 hours earlier
> A.x[P,]
Value
## Not surprisingly there is no value returned
> T
[1] 1326106840
## Note that the returned time agrees that the returned time looks the same
as that in A()
## Make a check....
> Q <- as.POSIXct("Tue Jan 10 00:00:40 2012", format="%a %b %d %T %Y")
> A.x[Q,]
Value
2012-01-10 00:00:40 0.7842
>
I am hopelessly confused. Is there is some sort of transformation as the
POSIXct is changed to numertic on return from sapply?
cheers
Worik
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