You used the lines function to plot the data. Of course it is going to show straight sloped lines between points.
On March 19, 2026 7:00:00 AM PDT, "송상은" <[email protected]> wrote: >Dear R-help members, > >Hello, >I am studying kernel regression and experimenting with the ksmooth() >function in R. > >When using a box kernel, the kernel function is an indicator function >(weight = 1 inside the bandwidth and 0 outside). Based on this definition, >I expected the Nadaraya–Watson estimator to produce a step-like function: >the estimate should remain constant while the set of included points is >unchanged, and then jump when a point enters or leaves the bandwidth window. > >However, when I run the following code using the cars dataset: > >par(mfrow=c(1,1)) >with(cars, { >plot(speed, dist) >lines(ksmooth(speed, dist, "normal", bandwidth = 2), >col = "blue", lwd = 3) >lines(ksmooth(speed, dist, "box", bandwidth = 2), >col = "darkorange", lwd = 3) >}) >legend("topleft", c("Normal Kernel with h=2", "Box Kernel with h=2"), >lwd = c(2,2), >col = c("blue","darkorange"), cex = 2) > >the curve produced by the box kernel (dark orange) appears to contain >diagonal line segments rather than the step-like shape I expected. I have >attached the resulting plot for reference. > >My understanding is that the theoretical estimator should behave like a >step function because the kernel weights are either 0 or 1. Therefore, I >was wondering whether the diagonal segments arise from how ksmooth() >evaluates the estimator on a grid of x values and then connects those >points with straight lines for plotting, or if there is another >implementation detail that explains this behavior. > >Could you please clarify whether this is expected behavior? > >Thank you very much for your time. > >Best regards, >Sangeun Song -- Sent from my phone. Please excuse my brevity. [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide https://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
