Sorry, I made two mistakes. The first was matching the female with the male. The second was 2 variables should be selected randomly every time.
Followed is a revised copy: ## Import data. moms <- read.delim("females.txt", sep =" ", stringsAsFactors = FALSE, header = TRUE) dads <- read.delim("males.txt", sep =" ", stringsAsFactors = FALSE, header = TRUE) ## Mate. ## Each male doesn't mate twice. parents <- cbind(moms, dads[sample(nrow(dads), nrow(moms)),]) ## Assign output data frame. ## The matrix "resultscheck" will be used to check the random selections. output_offspring <- as.data.frame(matrix("", nrow = nrow(moms), ncol = 6), stringsAsFactors = FALSE) resultscheck <- as.data.frame(matrix("", nrow = nrow(moms), ncol = 6), stringsAsFactors = FALSE) ## Randomly select two variables both from moms and dads. for(i in 1:nrow(parents)) { selection <- c(1, sample((2:5),2), 6, sample((7:10),2)) output_offspring[i,] <- parents[1,selection] resultscheck[i,] <- selection } ## Show the random selections. resultscheck ## Output. write.table(output_offspring,"offspring_7.txt",row.names=F,col.names=c("momID","A1","A2","dadID","A3","A4"),quote=F) ----- A R learner. -- View this message in context: http://r.789695.n4.nabble.com/sample-tp2218361p2221328.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.