# Re: [R] superimpose density line over hist

From: Martin Maechler <maechler_at_stat.math.ethz.ch>
Date: Wed 14 Dec 2005 - 21:54:48 EST

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

........

```    Romain> A few comments :
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

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