Your last step will either be a single number (not really a sampling
operation) or a
non-positive number. So at best you really only have an number that
depends
entirely on the prior sequence of draws.
--
David.
On May 28, 2009, at 8:21 AM, jos matejus wrote:
Dear Ritchie and David,
Thanks very much for your advice. I had thought of this potential
solution, however it doesn't really fullfill my second criteria which
is that once a particular cell has been sampled, the row and column of
that cell can't be sampled from subsequently. In other words, the next
sample would be taken from a 5x5 matrix, and then a 4x4 matrix and so
on until I have my 6 values.
I will keep thinking!
Cheers
Jos
2009/5/28 David Winsemius <dwinsem...@comcast.net>:
On May 28, 2009, at 6:33 AM, jos matejus wrote:
Dear R users,
I have a matrix of both negative and positive values that I would
like
to randomly sample with the following 2 conditions:
1. only sample positive values
2. once a cell in the matrix has been sampled the row and column of
that cell cannot be sampled from again.
#some dummy data
set.seed(101)
dataf <- matrix(rnorm(36,1,2), nrow=6)
I can do this quite simply if all the values are positive by using
the
sample function without replacement on the column and row indices.
samrow <- sample(6,replace=F)
samcol <- sample(6,replace=F)
values <- numeric(6)
for(i in 1:6){
values[i] <- dataf[samrow[i], samcol[i]]
}
However, I am not sure how to include the logical condition to only
include postitive values
Any help would be gratefully received.
Jos
M <- matrix(rnorm(36),nrow=6)
M[M[,]>0]
[1] 1.65619781 0.56182830 0.23812890 0.81493915 1.01279243
1.29188874
0.64252343 0.53748655 0.31503112
[10] 0.37245358 0.07942883 0.56834586 0.62200056 0.39478167
0.02374574
0.04974857 0.56219171 0.52901658
sample(M[M[,]>0],6,replace=F)
[1] 0.56834586 0.07942883 0.31503112 0.62200056 0.02374574 0.64252343
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
______________________________________________
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.
