From: Duncan Murdoch <murdoch_at_stats.uwo.ca>

Date: Mon 25 Sep 2006 - 18:03:26 GMT

R-help@stat.math.ethz.ch 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. Received on Tue Sep 26 04:06:43 2006

Date: Mon 25 Sep 2006 - 18:03:26 GMT

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
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch 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.
*

R-help@stat.math.ethz.ch 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. Received on Tue Sep 26 04:06:43 2006

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