Thanks Greg for your response. Is there a work around? Of course this begs the question as to Why is attach part of the sample session in App. A of the introductory manual? All the commands are directly from App. A. Is it possible the configuration of R on my computer is not in accord with acceptable practice? I.e. Could my configuration be set so that attach works as App. A intends? If not then App. A needs to be changed to replace attach. If so, then App. A needs to provide instructing on appropriate configuration of R for newbies.
Stephen Meskin Sent from my iPad > On May 29, 2014, at 1:06 PM, Greg Snow <538...@gmail.com> wrote: > > This is a warning and in your case would not be a problem, but it is > good to think about and the reason why it is suggested that you avoid > using attach and be very careful when you do use attach. What is > happening is that you first created a vector named 'x' in your global > workspace, you then create a data frame that contains a column that is > a copy of 'x' that is also named 'x' and the data frame also has > another column named 'y'. You then later attach the data frame to the > search list (if you run the 'search()' command you will see your > search list). This is convenient in that you can now access 'y' by > typing its name instead of something like 'dummy$y', but what happens > if you just type x? The issue is that there are 2 objects on your > search path with that same name. For your example it will not matter > much because they have the same value, but what if you run a command > like 'x <- 3', now you will see a single value instead of a vector of > length 20 which can lead to hard to find errors. This is why R tries > to be helpful by warning you that there are multiple objects named 'x' > and therefore you may not be accessing the one that you think. If you > use attach without being careful it is possible to plot (or regress or > ...) one variable from one dataset against another variable from a > completely unrelated dataset and end up with meaningless results. So, > if you use attach, be careful. You may also want to look at the > followng functions for help with dealing with these issues: conflicts, > find, get, with, within > >> On Wed, May 28, 2014 at 11:55 PM, Stephen Meskin <actu...@umbc.edu> wrote: >> While following the suggestion in the manual "An Introduction to R" to >> begin with Appendix A, I ran into the problem shown below about 3/4 of >> the way down the 1st page of App. A. >> >> After using the function /attach/, I did not get visible columns in the >> data frame as indicated but the rather puzzling message emphasized below. >> >> I am running R version 3.1.0 (2014-04-10) using Windows XP. Thanks in >> advance for your help. >> >>>> x<-1:20 >>>> w<-1+sqrt(x)/2 >>>> dummy<-data.frame(x=x, y=x+rnorm(x)*w) >>>> dummy >>> x y >>> 1 1 2.885347 >>> ... >>>> fm<- lm(y ~ x, data=dummy) >>>> summary(fm) >>> >>> Call: >>> ... >>>> fm1<- lm(y ~ x, data=dummy,weight=1/w^2) >>>> summary(fm1) >>> >>> Call: >>> ... >>>> attach(dummy) >>> *_The following object is masked _by_ .GlobalEnv: >>> >>> x_**_ >>> _* >> >> -- >> /Stephen A Meskin/, PhD, FSA, MAAA >> Adjunct Assistant Professor of Mathematics, UMBC >> >> **// >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> 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. > > > > -- > Gregory (Greg) L. Snow Ph.D. > 538...@gmail.com > ______________________________________________ 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.
