Fred Jean wrote: > > Dear list > > I'm trying to solve the following problem since 2 days with no success. > Could someone help a newbie, please ? > > I have a dependant variable which is diameter of shell, and two factors > which are level on the beach (3 levels 'B', 'E' and 'H') and a hydrodynamics > indice (3 levels 1, 2 and 3) > > To study diameter variations according to these factors, I may use something > like : > > mod <- lm(diameter ~ level * hydro) > > When I want to look at the graphical results of such a model on a > scatterplot, I use > > > plot(diameter ~ as.integer(hydro), col = as.integer(level)) > > and to draw the model lines : > > > lines(as.integer(hydro)[lev=='B'], predict(mod)[lev=='B'], col = 1) > > lines(as.integer(hydro)[lev=='E'], predict(mod)[lev=='E'], col = 1) > > lines(as.integer(hydro)[lev=='H'], predict(mod)[lev=='H'], col = 1) > > But sometimes, the lines are not drawn in the order of the levels of hydro but > as a *zigzag* and lines() commands seem to draw lines going from level 1 > to level 3 and then back to level 2 of the x axis (hydro)
All data must be sorted according to the hydro variable. > I hope this description is comprehensible. Could someone explain me how to > avoid this ? > > Many thanks for giving me some of your time. You are looking for interaction.plot(), I think, see ?interaction.plot for details. Uwe Ligges ______________________________________________ [EMAIL PROTECTED] mailing list http://www.stat.math.ethz.ch/mailman/listinfo/r-help
