Deriving Samples from specific, not implemented PDF for a QQ-Plot
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