The problem is that 90% of your data sit on the boundary. Loess is a nearest neighbor smoother (using (100 x span) % of the data to estimate at each point). If you call loess() directly with span=2/3 (the default in scatter.smooth), or something smaller than about 0.91, you'll see that it has trouble.
Strangely, if you set span=.8, scatter.smooth() will also complain, but not at the default span... (Re-generating the data yet again does trigger the warnings, so seems like it does catches things some of the time.) For your second example, I think loess becomes undefined when the span is set too small (and 1/n is surely too small): You are asking the algorithm to take the nearest 1/n of the data to do the smooth. You would think that should just mean _the_ nearest data point, but the problem is: > n <- 100 > 1 / n < 1 [1] TRUE so you're asking the algoithm to take fewer than 1 data point to estimate at each point. The warnings you see for that example is pointing you in the right direction. Andy > From: Jean Eid > > I have a problem either understanding what loess is doing or > that loess > has a problem itself. > > As the x-axis variables become more concentrated on a > particular point,the > estimated loess tends to zero????. the examples below show what i am > talking about, why is that? my intution tells me > that it should tend to the mean of the variable which is been > smoothed. > > Here's a worked up example > > x <- c(seq(0,100), rep(100,1000)) > y <- rnorm(length(x), mean=10, sd=2) > scatter.smooth(x,y) > > > > Although it does give warnings, I don't understand why it is > giving the > estimate as zero. > > > another example would be > > x <- seq(0,100) > y <- rnorm(length(x), mean=50, sd=2) > scatter.smooth(x,y, span=1/length(x)) > > > shoudn't this give just the points at which the smoothing algorithm is > applied? > > > > thank you > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > > ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
