Dear List, I am trying to sub-sample some data by taking a data point every x minutes. The data contains missing values, and I would like to take the sub-sample that maximizes the number of valid points in the sample. I.e. minimizes the number of NA's in the data set. For example, given the following: da<-seq(Sys.time(),by=1,length.out=10) x<-c(1,2,NA,4,NA,6,NA,8,9,10) mydata<-data.frame(da,x) If I wanted to take a subsample every 2 seconds, I would have the following two possible answers: answer1: 2,4,NA,8 answer2: 1,NA,NA,7 I would like a function that would choose between these and obtain the one with the fewest missing values. In my real dataset I have multiple variables collected every second and I would like to subsample it every 5, 10, and 15 minutes. I appreciate your help. Tim Tim Clark Department of Zoology University of Hawaii