as.numeric() doesn't convert factors to the explicit value, nor should it. Under what you're expecting, ff you have a factor where the levels are "Female" and "Male", using as.numeric() wouldn't produce anything meaningful.
However, as.numeric() does something much smarter. It converts "Female" to 1, and "Male" to 2. More generally, if you have n levels, it will produce a vector of values between 1 and n. This is referred to as the 'internal coding.' If you want to convert your height and bmi variables to their numeric values, you need to do > as.numeric(as.character(height)) This will get you around the internal coding. -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of deanj2k Sent: Friday, May 15, 2009 7:58 AM To: r-help@r-project.org Subject: [R] help with as.numeric hi everyone, wondering if you could help me with a novice problem. I have a data frame called subjects with a height and weight variable and want to calculate a bmi variable from the two. i have tried: attach(subjects) bmi <- (weight)/((height/100)^2) but it comes up with the error: Warning messages: 1: In Ops.factor(height, 100) : / not meaningful for factors 2: In Ops.factor((weight), ((height/100)^2)) : / not meaningful for factors I presume that this means the vectors height and weight are not in numeric form (confirmed by is.numeric) so i changed the code to: bmi <- (as.numeric(weight))/((as.numeric(height)/100)^2) but this just comes up with a result which doesnt make sense i.e. numbers such as 40000 within bmi vector. Ive looked at as.numeric(height)/as.numeric(weight) and these numbers just arnt the same as height/weight which is the reason for the incorrect bmi. Cant anyone tell me where I am going wrong? Its quiet frustrating because I cant understand why a function claiming to convert to numeric would come up with such a bizarre result. -- View this message in context: http://www.nabble.com/help-with-as.numeric-tp23558326p23558326.html Sent from the R help mailing list archive at Nabble.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. =================================== P Please consider the environment before printing this e-mail Cleveland Clinic is ranked one of the top hospitals in America by U.S. News & World Report (2008). Visit us online at http://www.clevelandclinic.org for a complete listing of our services, staff and locations. Confidentiality Note: This message is intended for use\...{{dropped:13}} ______________________________________________ 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.
