[R] Can't mix high level and low level plot functions.

[Duncan Murdoch]

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
> 
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