If I understood correctly, you need weighted sampling. Try 'prob' argument from 'sample'. For your example:
n <- 10 ntype <- rbinom(n, 1, 0.5) myProbs <- rep(1/10, 10) # equally likely myProbs[ which(ntype == 0)] <- 0.75/7 # Divide so the sum will be 1.0 myProbs[ which(ntype == 1)] <- 0.25/3 sample(ntype,3, prob=myProbs) On 5 March 2014 15:20, Thomas <thomas.ches...@nottingham.ac.uk> wrote: > I have a matrix where each entry represents a data subject's type, 1 or 0: > > n <- 10 > ntype <- rbinom(n, 1, 0.5) > > and I'd like to sample say 3 subjects from ntype where those subjects who > are Type 1 are selected with probability say 0.75, and Type 0 with (1-0.75). > (So the sample would produce a list with three indices each referring to a > position within ntype.) > > Can anyone suggest a way to do this please? > > Thank you, > > Thomas Chesney > This message and any attachment are intended solely for the addressee and > may contain confidential information. If you have received this message in > error, please send it back to me, and immediately delete it. Please do not > use, copy or disclose the information contained in this message or in any > attachment. Any views or opinions expressed by the author of this email do > not necessarily reflect the views of the University of Nottingham. > > This message has been checked for viruses but the contents of an attachment > may still contain software viruses which could damage your computer system, > you are advised to perform your own checks. Email communications with the > University of Nottingham may be monitored as permitted by UK legislation. > > ______________________________________________ > 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.