When I use the code as.Date(0) the I get : "1970-01-01". My question is why it is like that? help file on as.Date seems to give no light on that. Can anyone clarify me? Regards, Send instant messages to your online friends http://uk.messenger.yahoo.com [[alternative HTML version deleted]]
On Thu, 3 Jul 2008, Ron Michael wrote:> When I use the code as.Date(0) the I get : "1970-01-01". My question is > why it is like that? help file on as.Date seems to give no light on > that. Can anyone clarify me?In R, "Date" objects are stored internally as the number of days since 1970-01-01 (typically the epoch on Unix systems): ## today dd <- as.Date("2008-07-03") dd ## number of days since 1970-01-01 dn <- as.numeric(dd) dn ## In base R, you can reverse this if you specify the origin used as.Date(dn, origin = "1970-01-01") ## If you load package "zoo", this is made the default library("zoo") as.Date(dn) The idea of the zoo implementation is that you can switch back and forth between the "Date" and numeric representation. The implementation in base R, on the other hand, wants to be agnostic to the origin used and hence sets no default for that argument. hth, Z> ?? > Regards, > > Send instant messages to your online friends http://uk.messenger.yahoo.com > [[alternative HTML version deleted]] > >
Ron Michael wrote:> When I use the code as.Date(0) the I get : "1970-01-01". My question is why it is like that? help file on as.Date seems to give no light on that. Can anyone clarify me? >Which version of R is this? R version 2.7.1 (2008-06-23) ...> as.Date(0)Error in as.Date.numeric(0) : 'origin' must be supplied and the help page has the explanation. Internally, Date objects are represented as days since 1970-01-01, and you can still exploit that with> structure(0,class="Date")[1] "1970-01-01" although you really shouldn't need to have and shouldn't have to use that knowledge. [By the way, there used to be a way to see the current help pages on the web, but I can't remember how. Searching for as.Date via the R search sites doesn't help either (interesting set of sponsored links from Google though...), and the Wiki interface to help pages appears to be broken.]> > Regards, > > Send instant messages to your online friends http://uk.messenger.yahoo.com > [[alternative HTML version deleted]] >-- O__ ---- Peter Dalgaard ?ster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907