Thank you! On Sat, May 9, 2009 at 11:31 AM, Ted Harding <ted.hard...@manchester.ac.uk> wrote: > On 09-May-09 16:10:42, Jacques Wagnor wrote: >> Dear List, >> When I plot a histogram with 'freq=FALSE' and overlay the >> histogram with a normal pdf curve, everything looks as expected, >> as follows: >> >> x <- rnorm(1000) >> hist(x, freq=FALSE) >> curve(dnorm(x), add=TRUE, col="blue") >> >> What do I need to do if I want to show the frequencies (freq=TRUE) >> with the same normal pdf overlay, so that the plot would still look >> the same? >> >> Regards, >> Jacques > > Think first about how you would convert the histogram densities > (heights of the bars on the "density" scale) into histogram frequencies. > > Density * (bin width) * N = frequency > > where N = total number in sample. Then all you need to is multiply > the Normal density by the same factor. To find out the bin width, > take the difference between succesive values of the "breaks" component > of the histogram. One way to do all this is > > N <- 1000 > x <- rnorm(N) > H <- hist(x, freq=TRUE) ## This will plot the histogram as well > dx <- min(diff(H$breaks)) > curve(N*dx*dnorm(x), add=TRUE, col="blue") > > Ted. > > -------------------------------------------------------------------- > E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk> > Fax-to-email: +44 (0)870 094 0861 > Date: 09-May-09 Time: 17:31:03 > ------------------------------ XFMail ------------------------------ >
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