On Sep 6, 2013, at 12:34 , Gerrit Eichner wrote: > Hello, Francesco, > > these could be considered as two of the central questions in statistics in > general ... but they do not necessarily have anything to do with R. > > Regards -- Gerrit
Yes. However, since it is Friday and my brain is fried from the morning lecture anyway: If you can represent the (finite) sample space in R, you can also do probability calculations in R. Conditioning corresponds to subsetting the sample space. E.g., for a double dice throw (D1,D2) you can find > twodice <- expand.grid(d1=1:6,d2=1:6) > with(twodice, mean(d1==5)) [1] 0.1666667 > with(subset(twodice,d1+d2==8), mean(d1==5)) [1] 0.2 > with(subset(twodice,d1+d2==11), mean(d1==5)) [1] 0.5 I.e. P(D1=5) = 1/6 P(D1=5 | D1+D2=8) = 1/5 P(D1=5 | D1+D2=11) = 1/2 The above works for symmetric probability spaces. For general finite spaces, include a vector of probabilities and do something like this: > twodice$p <- 1/nrow(twodice) > with(subset(twodice,d1+d2==11), sum(p[d1==5])/sum(p)) [1] 0.5 - Peter D. > > On Fri, 6 Sep 2013, Francesco Miranda wrote: > >> how can i calculate the probability of occurrence of an event and the >> probability of an event upon the occurrence of another event. >> P (A) and P (A | B) .. >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-help@r-project.org 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@r-project.org 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. -- Peter Dalgaard, Professor Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-help@r-project.org 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.
