Dear list I wish to extract from a population genotypized for a group of SNP a subsample of the same population of size n with similar allele frequencies. I approached the problem with sample() function (subdataset is the size of my extracted sample and df is the name of the initial data.frame) mysample<-df[sample(1:nrow(df),subdataset,replace=F),] Then I tested that the frequencies of each allele in mysample are not statistically different respect to the initial dataset by mean of prop.test This seems to work but do you know if there is a package that can do the same thing allowing for example a more strict control? -- Guido Leoni National Research Institute on Food and Nutrition (I.N.R.A.N.) via Ardeatina 546 00178 Rome Italy tel + 39 06 51 49 41 (operator) + 39 06 51 49 4498 (direct) [[alternative HTML version deleted]]