On 09-Dec-09 23:52:20, Gaurav Moghe wrote: > Hello, > This is a problem for which there seem to be several solutions online, > but not really. My question was about plotting a curve over the > histogram. > All the previous posts and messages talk about generating a *density > histogram* using (freq=F) and then plotting the density curve. > However, I find that that seriously distorts my data and the plot > becomes confounding to the viewer. > > I was wondering if there's a way to do the following 2 things: > 1) Plot both histogram and the overlying frequency curve in one plot > 2) Plot multiple frequency curves in a single plot > > I have been using the "hist" function for my job. > > I'd appreciate if anyone could help me with the solution > > Thanks, > Gaurav
You presumably mean that the viewer expects to see a histogram of counts, with the corresponding estimated curve of expected counts for each bin-interval (NB *not* density!!) plotted over it. The following is an example of how to achieve this. set.seed(54321) N <- 1000 x <- rnorm(N) H <- hist(x,breaks=50) dx <- (H$breaks[2]-H$breaks[1]) m <- mean(x) s <- sd(x) x0 <- H$breaks x1 <- c(x0[1]-dx/2,x0+dx/2) y0 <- H$counts lines(x1,N*dnorm((x1 - m)/s)*dx) In the above, m and s are the estimated Mean and SD of the fitted Normal distgribution. Therefore the estimated *density* at x is dnorm((x - m)/s)*dx and a good approximation to the probability contained in a given bin whose midpoint is at x1 is dnorm((x1 - m)/s)*dx, where dx is the width of the bin. The total sample size being N, the expected count for that bin is N*dnorm((x1 - m)/s)*dx. With this explanation, the above should now be clear! Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861 Date: 10-Dec-09 Time: 00:51:58 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.