Systematic Sampling in R
SampleBy in the doBy package that was useful in R is not supported. I have created sample.by systematic sampling function as below. ^^ ## usage : sample.by(data_as_dataframe, number_of_column, ratio_of_sample) ## returns a list of sample.df and rest.df sample.by <- function(df, by.col.loc=1, prop=0.1) { sample.df <- data.frame() rest.df <- data.frame() dat <- split(df, df[by.col.loc]) for(i in 1:NROW(dat)) { idx <- sample(c(rep(1,n<-round(NROW(dat[[i]]) * prop)), rep(2,NROW(dat[[i]]) - n))) sample.df <- rbind(sample.df, dat[[i]][idx==1,]) rest.df <- rbind(rest.df, dat[[i]][idx==2,]) } list(sample.df=sample.df[sample(NROW(sample.df)),], rest.df=rest.df[sample(NROW(rest.df)),]) } ## example sample.by(iris, 5, 0.7)