You have to understand the ``scope'' argument to add1. As Rui Barradas points out, that argument expects a formula, but you pass it a data frame, YET you only get two warnings. You should practice having that feel strange to you, and having it make you investigate:
1- Why did you not have to give add1 a formula, even though Rui Barradas said you did? 2- Why did add1 warn you about the response, ``E'', appearing on ``the right-hand side''? 3- Why did add1 warn you about a ``problem with term 4 in model.matrix''? As a starter for your answering these questions, describe what you get from this: formula(mydata) Below are some questions to might answer as a follow-up to help yourself answer the above questions. 1- What might add1 have done when you gave it a data frame for its scope argument? 2- How does the location of the linear regression's response term explain the first warning? 3- What does ``model.matrix'' do anyway? 4- What is ``term 4'' in a model matrix, and how does it differ from column 4 of a matrix? 5- How does this last answer help explain the second warning? 6- How does the abscence of an ``A'' on right-hand side explain why the result of add1 did not have an ``A'' row? Best, Mario On Fri, Jan 4, 2013 at 6:53 PM, dada <pa...@nottingham.ac.uk> wrote: > Hi > > I am trying to build a regression model. My data looks like this: > > A B C D E > 1 1 1 2.57 5 > 2 0 0 1.64 3 > 0 5 1 4.8 1 > 1 3 0 3.56 168 > 1 1 1 2.13 1 > 0 3 1 5 168 > 2 0 0 7.75 28 > 4 0 2 2.85 168 > 3 0 1 1.89 6 > 1 1 1 2.33 3 > 3 2 2 1.77 168 > 1 0 0 1.38 0.04 > 0 6 1 4.57 168 > 2 2 2 2.86 1 > 3 1 1 4.11 168 > 3 0 2 3 84 > 1 1 1 2.5 56 > > where E is a response variable and A, B, C, D are predictor variables. > Below > are commands which I enter in R: > > str (mydata) > mydata.lm = lm (E ~ 1, data = mydata) # to create a blank model > add1(mydata.lm, mydata, test='F') # to add the best predictor variable to > the blank model > > However at this point the message appears: > > Warning messages: > 1: In model.matrix.default(Terms, m, contrasts.arg = object$contrasts) : > the response appeared on the right-hand side and was dropped > 2: In model.matrix.default(Terms, m, contrasts.arg = object$contrasts) : > problem with term 4 in model.matrix: no columns are assigned > > What does it mean ? Could you please help ? > > > > > > > -- > View this message in context: > http://r.789695.n4.nabble.com/building-a-regression-model-tp4654701.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. [[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.
