From: Liaw, Andy <andy_liaw_at_merck.com>

Date: Wed 09 Aug 2006 - 04:10:26 EST

R-help@stat.math.ethz.ch 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. Received on Wed Aug 09 04:19:10 2006

Date: Wed 09 Aug 2006 - 04:10:26 EST

> On Fri, 2006-08-04 at 12:46 -0400, Daniel Gerlanc wrote:

*> > Hello all,
**> >
**> > Consider the following problem:
**> >
**> > There is a matrix of probabilities:
**> >
**> > > set.seed(1)
**> > > probs <- array(abs(rnorm(25, sd = 0.33)), dim = c(5,5),
**> dimnames =
**> > > list(1:5, letters[1:5])) probs
**> > a b c d e
**> > 1 0.21 0.27 0.50 0.0148 0.303
**> > 2 0.06 0.16 0.13 0.0053 0.258
**> > 3 0.28 0.24 0.21 0.3115 0.025
**> > 4 0.53 0.19 0.73 0.2710 0.656
**> > 5 0.11 0.10 0.37 0.1960 0.205
**> >
**> > I want to sample 3 values from each row.
**> >
**> > One way to do this follows:
**> >
**> > index <- 1:ncol(probs)
**> >
**> > for(i in 1:nrow(probs)){
**> >
**> > ## gets the indexes of the values chosen
**> >
**> > sample(index, size = 3, replace = TRUE, prob = probs[i, ])
**> >
**> > }
**> >
**> > Is there a another way to do this?
**> >
**> > Thanks!
**>
**> > t(apply(probs, 1, function(x) sample(x, 3)))
**> [,1] [,2] [,3]
**> 1 0.210 0.5000 0.0148
**> 2 0.258 0.0053 0.1300
**> 3 0.025 0.2800 0.3115
**> 4 0.190 0.5300 0.2710
**> 5 0.196 0.1000 0.1100
*

Hmm... If I read Daniel's code (which is different from his description) correctly, that doesn't seem to be what he wanted. Perhaps something like this:

apply(probs, 1, function(p) sample(1:ncol(probs), 3, replace=TRUE, prob=p))

Andy

> See ?apply and ?t

*>
**> HTH,
**>
**> Marc Schwartz
*

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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. Received on Wed Aug 09 04:19:10 2006

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