On 9/25/2006 1:56 PM, Lothar Botelho-Machado wrote: > Hey R-Comunity, > > > I'd like to print out an histogram of some experimental data and add a > smooth curve of a normal distribution with an ideally generated > population having the same mean and standard deviation like the > experimental data. > > > The experimental data is set as vector x and its name is set to > group.name. I paint the histogram as follows: > > hist(data, freq=FALSE, col="lightgrey", ylab="Density", xlab=group.name) > > > > First I did the normal distribution curve this way: > > lines(x, dnorm(x, mean=mean(x), sd=sd(x)), type="l", lwd=2) > > This curve just uses as many values as there are in x. When using small > amounts of sample populations the curve looks really shaky.
This is generally the right way to do it, but you likely want to use a different variable for the first two occurrences of x, e.g. x0 <- seq(from=min(x), to=max(x), len=200) lines(x0, dnorm(x0, mean=mean(x), sd=sd(x)), type="l", lwd=2) Duncan Murdoch > > > I tried this one using a high level plot function as well: > > curve(dnorm, n=10000, add=TRUE, xlim=range(x)) > > The advantage is, now I can set an ideal population of 10000 to get the > ideal curve really smooth. But the big disadvantage is, I don't know how > to add "mean=mean(x), sd=sd(x)" arguments to it? It says that it can't > mix high level with low level plot functions when I try to set some kind > of parameter like "n=10000" to the low level function, it says that > there ain't enough x values. > > So my question is, how to get a smooth curve placed of dnorm over an > histogram of sample data, ideally by using the curve method? > > > TIA, > Lothar Rubusch > > ______________________________________________ > [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 > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ [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 and provide commented, minimal, self-contained, reproducible code.
