It probably happens because plot(formula) makes one call to terms(formula) to analyze the formula. terms() says there is one variable in the formula, the response, so plot(x~x) is the same a plot(seq_along(x), x). If you give it plot(~x) , terms() also says there is one variable, but no response, so you get the same plot as plot(x, rep(1,length(x))). This is also the reason that plot(y1+y2 ~ x1+x2) makes one plot of the sum of y1 and y2 for each term on the right side instead of 4 plots, plot(x1,y1), plot(x1,y2),plot(x2,y1), and plot(x2,y2).
One could write a plot function that called terms separately on the left and right sides of the formula. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf > Of Tal Galili > Sent: Wednesday, November 06, 2013 8:40 AM > To: r-help@r-project.org > Subject: [R] Basic question: why does a scatter plot of a variable against > itself works like > this? > > Hello all, > > I just noticed the following behavior of plot: > x <- c(1,2,9) > plot(x ~ x) # this is just like doing: > plot(x) > # when maybe we would like it to give this: > plot(x ~ c(x)) > # the same as: > plot(x ~ I(x)) > > I was wondering if there is some reason for this behavior. > > > Thanks, > Tal > > > > ----------------Contact > Details:------------------------------------------------------- > Contact me: tal.gal...@gmail.com | > Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) | > www.r-statistics.com (English) > ---------------------------------------------------------------------------------------------- > > [[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. ______________________________________________ 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.
