[R] Howto fit normal curve into histogram using GGPLOT2

[ONKELINX, Thierry]

That is not very complex with densities instead of counts.

library(ggplot2)
ggplot(mtcars, aes(x = mpg)) + 
	geom_histogram(aes(y = ..density..), fill = "red") + 
	stat_function(
		fun = dnorm, 
		args = with(mtcars, c(mean = mean(mpg), sd = sd(mpg)))
	) + 
	scale_x_continuous("Miles per gallon") + 
	opts(title = "Histogram with Normal Curve") 

Or with a bit more effort to get the counts.

ggplot(mtcars, aes(x = mpg)) + 
	geom_histogram(fill = "red") + 
	stat_function(
		fun = function(x, mean, sd, n){
			n * dnorm(x = x, mean = mean, sd = sd)
		}, 
		args = with(mtcars, c(mean = mean(mpg), sd = sd(mpg), n
= length(mpg)))
	) + 
	scale_x_continuous("Miles per gallon") + 
	opts(title = "Histogram with Normal Curve")

HTH

Thierry

PS Have a look at the ggplot2 website (http://had.co.nz/ggplot2/).
You'll find tons of examples with the code the generate them.

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens Gundala Viswanath
Verzonden: woensdag 2 september 2009 16:37
Aan: r-help at stat.math.ethz.ch
Onderwerp: [R] Howto fit normal curve into histogram using GGPLOT2

Currently, I am doing it this way.

x <- mtcars$mpg
h<-hist(x, breaks=10, col="red", xlab="Miles Per Gallon",
   main="Histogram with Normal Curve")
xfit<-seq(min(x),max(x),length=40)
yfit<-dnorm(xfit,mean=mean(x),sd=sd(x))
yfit <- yfit*diff(h$mids[1:2])*length(x) lines(xfit, yfit, col="blue",
lwd=2)

But since, ggplot2  has more appealing graphics, I wonder how can it be
done.

-G.V.

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