It doesn't have anything to do with attach (which is naughty in other ways!) rather it's the internal representation of categorical variables (R speak: factors) that store each level as an integer for memory efficiency but print things with string levels so they look nice to the user.
You'll note there's a 1-to-1 match between Ctl-1 an Trt-2 in your data. The funny business (best I reckon) is that use of $ which down-grades your data to its internal representation as a numeric (integer) vector. But yes, you should avoid attach anyways. M On Jan 27, 2012, at 6:03 AM, Олег Девіняк <o.devin...@gmail.com> wrote: > I am confused whether Student's sleep data "show the effect of two > soporific drugs" or Control against Treatment (one drug). The reason > is the next: >> require(stats) >> data(sleep) >> attach(sleep) >> extra[group==1] > numeric(0) >> group > [1] Ctl Ctl Ctl Ctl Ctl Ctl Ctl Ctl Ctl Ctl Trt Trt Trt Trt Trt Trt Trt Trt > Trt > [20] Trt > Levels: Ctl Trt >> sleep$group > [1] 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 > Levels: 1 2 > > Does some package overwrite my attach()? I am worried mostly in the > right performance of my code by others. So have the attach() to be > avoided? > Thanks for answers! > > ______________________________________________ > 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. ______________________________________________ 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.
