The book came out in 2002 and a lot has happened with R in the time since then. In particular it is now possible for R to have 'lazy loading' of objects. If the person setting up the package has used this option (as they all now should), when the package is loaded R essentially is made aware that the data (and other) objects are there, so it is visible, but it is only read into memory if it is used. The little tag that alerts R to the existence of the object and triggers the automatic loading on demand is called a 'promise' and the action itself is called a 'delayed assign'.
Previously this all had to be done manually. data() could be used either to discover what data objects were available in packages, or to load them in to memory. Many old-style packages still require you to do this. There are cases where it is justified, I suppose, but they are quite hard to think of... With R you have to keep abreast of developments, and it's all happening pretty fast. Bill Venables. PS Since you are new to R, it is not considered very friendly to send messages to the R groups anonymously. Bill Venables CSIRO Laboratories PO Box 120, Cleveland, 4163 AUSTRALIA Office Phone (email preferred): +61 7 3826 7251 Fax (if absolutely necessary): +61 7 3826 7304 Mobile: +61 4 8819 4402 Home Phone: +61 7 3286 7700 mailto:[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> http://www.cmis.csiro.au/bill.venables/ <http://www.cmis.csiro.au/bill.venables/> -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> ] On Behalf Of envisage Sent: Thursday, 8 November 2007 1:27 PM To: r-help@r-project.org Subject: [R] a newbie question about "data" hi, I am reading Modern Applied Statistics with S 4th ed。 page4 have these two lines: > library(MASS) > data(chem) # needed in R only but I find withou the line " data(chem)" I can still access chem, isn't it? is it unnecessary or something i missed here? thanks for the replay in advance.
______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
