Is your variable Clarity a categorical with 4 levels? Thus, the need for k-1 (3) dummies? Your error may be the result of creating k instead of k-1 dummies, but can't be sure from the example.
In R, you don't have to (unless you really want to) explicitly create separate variables. You can use the internal contrast functions. See ?contr.treatment Which is dummy coding by default. You can specify which group is the reference group. Alternatively, if you prefer effects coding, you can see ?contr.sum There are others as well. Tom Fletcher -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of whitaker m. (mw1006) Sent: Wednesday, December 16, 2009 8:59 AM To: r-help@r-project.org Subject: [R] Creating Dummy Variables in R Hi, I am trying to create a set of dummy variables to use within a multiple linear regression and am unable to find the codes within the manuals. For example i have: Price Weight Clarity IF VVS1 VVS2 500 8 1 0 0 1000 5.2 0 0 1 864 3 0 1 0 340 2.6 0 0 1 90 0.5 1 0 0 450 2.3 0 1 0 Where price is dependent upon weight (single value in each observation) and clarity (split into three levels, IF, VVS1, VVS2). I am having trouble telling the program that clarity is a set of 3 dummy variables and keep getting error messages, what is the correct way? Any helps is greatly appreciated. Matthew ______________________________________________ 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.
