问题
I know function combn can generate all the possible combinations. However, if the total number of members is large, this is really time-consuming and memory-consuming.
My goal is to randomly pick combinations from all the possible combinations. For example, I want 5000 distinct triple set of members from a pool of 3000 members. I think I don't need to generate all possible combinations and choose 5000 from them. But seems that R doesn't have a ready-to-use function to do this. So how to deal with this problem?
回答1:
This is not exactly what you need but perhaps it can get you started:
library(data.table) #to make the table easier
members=1:3000;
X=data.table(RUN=1:5000)
X<-X[,as.list(sample(members, 3)),by=RUN]
This will create 3 new columns that are randomly selected from the members vector. See them as IDs of each member.
I would do a check to see how many as unique using:
X[duplicated(X, by=c('V1','V2','V3'))]
Is this helping you at all?
来源：https://stackoverflow.com/questions/27125415/how-to-randomly-pick-a-number-of-combinations-from-all-the-combinations-efficien