Try this:
set.seed(1) n <- 100 first <- sample(0:1, n, replace = TRUE) second <- sample(0:1, n, replace = TRUE) sum(first == 1 & second == 1) / sum(first == 1 | second == 1) # The last could be written more compactly like this # as 1 and 0 will be treated as TRUE and FALSE by the # logical operators and then TRUE and FALSE will be # regarded as 1 and 0 by sum sum(first & second) / sum(first | second) On 9/22/06, Jacob van Wyk <[EMAIL PROTECTED]> wrote: > Dear UseRs > > I would like to show my students how to use "resampling" to solve the > following simple problem: > > If a family has two children of which one is a boy, what is the > probability that the other child is also a boy. > The answer is (obviously) 1/3, and can be show easily using the usual > methods. > But I would like to get the students to think of resampling, by doing > the following: > Flip two coins repeatedly, denoted 0 and 1 (1 for boy, say). Discard > those pairs that both contain 0. > >From those left over, count how many pairs are (1,1). > Divide this number by the number available to choose from (i.e. all > pairs, except (0,0)). > This will then give 1/3 (more or less of course). > > Can somebody help me to code this efficiently, or elegantly (and > smartly) in R, without loops etc. > It is intended for first year students that are only starting to learn > about statistics (or probability theory), and R of course. > > Thank you for your time. > Regards > Jacob > > > > > Jacob L van Wyk > Department of Statistics > University of Johannesburg, APK > P O Box 524 > Auckland Park 2006 > South Africa > Tel: +27 11 489 3080 > Fax: +27 11 489 2832 > > > > [[alternative HTML version deleted]] > > ______________________________________________ > [email protected] 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. > ______________________________________________ [email protected] 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.
