[R] Sample without replacement
Mark G Orr
morrct at andrew.cmu.edu
Wed Sep 22 17:29:15 CEST 2004
Hello, I have a simple problem (checked the archives and the appropriate
help pages, to no avail). I want to creat a vector that is length(2000).
The vector is to consist of two strings( "std" and "dev") with 1760 "std"s
and 240 "dev"s. Furthermore, for each element of the vector, i want the
selection of one of the strings to be approx. random. The end result will
be a vector with the following proportions: .12 "dev" and .88 "std".
My solution, below, almost works, but i don't get the exact desired
proportions:
sample.from.vector <- c(rep("std",1760),rep("dev",240))
make.vector <- rep(99,2000)
for (i in 1:2000){
make.vector[i] <- sample(sample.from.vector,1,replace=F)
}
As I understand the above code (which is not very well, obviously), each
iteration assigns one element from the sample.from.vector to the current
make.vector element; the element choosen from sample.from.vector is
tagged so that i is not selected again. However, after the loop,
make.vector contains, for example, 1758 stds and 242 devs. Each
iteration results in a different proportion of stds and devs (although
close to the desired, not right on).
Any help would be greatly apprecitated.
-Mark Orr
________________________________
Mark G. Orr
Postdoctoral Research Fellow
Dept. of Neuroscience
RM 825 Kennedy Center
Albert Einstein College of Medicine
Bronx, NY 10461
718-430-2610
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