try the following: B <- 10000 index <- rowSums(matrix(rbinom(B*2, 1, 0.5), ncol = 2)) sum(index == 2) / sum(index > 0)
I hope it helps. Best, Dimitris ---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/(0)16/336899 Fax: +32/(0)16/337015 Web: http://med.kuleuven.be/biostat/ http://www.student.kuleuven.be/~m0390867/dimitris.htm ----- Original Message ----- From: "Jacob van Wyk" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, September 22, 2006 12:57 PM Subject: [R] A simple resampling problem > 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. > Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm ______________________________________________ [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.
