On Mar 31, 2009, at 11:53 AM, Arndt Zimmermann wrote:
<trimmed superfluous white-space>
this is my first post to the R-help, so please don't be too strict.
Reproducible examples should not be too much to expect, since that is
requested in the posting guide and multiple other locations.
My problem concerns a QQ-Plot:
I want to show how well empirical samples match with a theoretical
distribution. The theoretical distribution has got several
parameters, but I
made it to fit via ML.
Anyway, the theoretical function gives me the density for a given
data point
x. As far as I'm aware, the qqplot (generic) function in R does only
take
data samples as Input.
How can I derive samples from the pdf? Am I right in the way I see the
problem?
Rather hard to tell, since you haven't described what I understand to
be a problem, nor described how you see it.
Or
How can I modify the qqplot function, (or rebuild for myself) to get
it
going?
It seems to be going fine for us. Did you break it?
I'm sure, this is very likely just a misunderstanding problem from
myself,
but anybody who can shed further light on this is very welcome.
Since you offer no examples, it is rather difficult to offer specific
advice. You should be able to use the sample function on a pdf by
assigning a vector of probabilities to the prob argument.
> mean(sample(seq(-2,2,by=0.2), size=100,
prob=dnorm(seq(-2,2,by=0.2)), replace=TRUE))
[1] -0.08
> sd(sample(seq(-2,2,by=0.2), siez=100, prob=dnorm(seq(-2,2,by=0.2)),
replace=TRUE))
[1] 0.911101
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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