# [R] superimpose density line over hist

Martin Maechler maechler at stat.math.ethz.ch
Wed Dec 14 11:54:48 CET 2005

```>>>>> "Romain" == Romain Francois <francoisromain at free.fr>
>>>>>     on Tue, 13 Dec 2005 15:40:59 +0100 writes:

........

Romain> - your code should be reproductible, otherwise it is useless. (that
Romain> recommandation is on the posting guide)

Romain> - that question is a top ten question on that list, go to the archive
Romain> and you will find answers. (also posting guide)
Romain> BTW, it should be a FAQ and what about an example of overlaying in hist
Romain> help page ?

What about the following one --- do also note the comments though!

set.seed(14)
x <- rchisq(100, df = 4)

## Comparing data with a model distribution should be done with qqplot()!
qqplot(x, qchisq(ppoints(x), df = 4)); abline(0,1, col = 2, lty = 2)

## if you really insist on using hist() ... :
hist(x, prob = TRUE, ylim = c(0, 0.2))
curve(dchisq(x, df = 4), col = 2, lty = 2, lwd = 2, add = TRUE)

Romain> - then if you want to superimpose an histogram and a density curve, they
Romain> should be on the same scale, it is not the case since you missed the
Romain> argument freq in your hist call, it should be :

R> hist(alnlength, freq=FALSE)

Romain> - Why do you simulate points to draw the density line ? Give a shot at :

R> curve(dchisq, df=4, col="red")

...........

Martin Maechler, ETH Zurich

```