On Wed, 3 Dec 2003, Arend P. van der Veen wrote: > Your recommendations have worked great. I have found both cut and > ifelse to be useful. > > I have one more question. When should I use factors over a character > vector. I know that they have different uses. However, I am still > trying to figure out how I can best take advantage of factors. > > The following is what I am really trying to do: > > colors <- c("red","blue","green","black") > y.col <- colors[cut(y,c(-Inf,250,500,700,Inf),right=F,lab=F)] > plot(x,y,col=y.col) > > Would using factors make this any cleaner? I think a character vector > is all I need but I thought I would ask. > > Thanks for your help, > Arend van der Veen
Arend - When setting the colors of plotted points, you definitely want a vector of character strings as the color names. "Factor" was invented so that regression and analysis of variance functions would properly recognize a grouping variable and not fit simply a linear coefficient to the integer codes. In the context of a linear (or similar) model, each factor or interaction has to be expanded from a single column of integer codes into a matrix of [0,1] indicator variables, with a separate column for each possible level of the factor. (I oversimplify a bit here: some columns are omitted, to keep the design matrix from being over-specified.) - tom blackwell - u michigan medical school - ann arbor - ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help