I am sorry I still don't understand. In the example you give the 'assign' vecotr is a vector of length 6 and there are indeed 6 columns in the data frame. But the formula only has two variables namely 'Month' and 'Wind'. Where do the values if the 'assign' vector come from? I see '0 1 1 1 1 2'. What is '1' an index to? '2'? Maybe I am get confused with what the term 'factors' does to the formula.
Thanks agiain for your help. Kevin ---- Peter Dalgaard <p.dalga...@biostat.ku.dk> wrote: > rkevinbur...@charter.net wrote: > > I am just curious. Every once and a while I see an attribute attached to an > > object called "assign". What meaning does this have? For example: > > > > dist ~ speed, data=cars > > > > forms a matrix like: > > > > num [1:50, 1:2] 1 1 1 1 1 1 1 1 1 1 ... > > - attr(*, "dimnames")=List of 2 > > ..$ : chr [1:50] "1" "2" "3" "4" ... > > ..$ : chr [1:2] "(Intercept)" "speed" > > - attr(*, "assign")= int [1:2] 0 1 > > > > The "dimnames" attribute is fairly self-explanatory. I just am not sure > > what the "assign" attribute means. > > It has to do with the mapping between terms of the formula and columns > of the design matrix: > > > str(model.matrix(Ozone~factor(Month)+Wind,data=airquality)) > num [1:116, 1:6] 1 1 1 1 1 1 1 1 1 1 ... > - attr(*, "dimnames")=List of 2 > ..$ : chr [1:116] "1" "2" "3" "4" ... > ..$ : chr [1:6] "(Intercept)" "factor(Month)6" "factor(Month)7" > "factor(Month)8" ... > - attr(*, "assign")= int [1:6] 0 1 1 1 1 2 > - attr(*, "contrasts")=List of 1 > ..$ factor(Month): chr "contr.treatment" > > I.e. columns 2:5 belong to the first non-intercept term, factor(Month). > (Notice that it is implicitly assumed that you have the corresponding > terms() output to hand, likewise for the "contrasts" attribute.) > -- > O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B > c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K > (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 > ~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ 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.
