search for: unique_x

...something obvious. Given: x=c(1,1,1,2,2,3,3,3) y=c(1:length(x)) dataframe=data.frame(x,y) I would like to convert this to a list for use with certain functions, where each entry of the list is a subsetted dataframe based on dataframe$x I can do this "brute force" by a for-next loop: unique_x=unique(dataframe$x) unique_x_N=length(unique_x) dataframe_to_list=vector(mode="list",length=unique_x_N) for(i in 1:unique_x_N) { dataframe_to_list[[i]]=subset(dataframe,x==unique_x[i]) } My R-gut is telling me there's a much more efficient way of doing this -- is it right? --j

I have a 280,000 x 11 matrix with various values and many NA values. What I would like to do is get a vector of every unique value in the matrix. For example: X = [ 1 2 NA 4 3 1 7 NA 2 ] Returns: Unique_X = [ 1, 2, 3, 4, 7] Thanks, Todd [[alternative HTML version deleted]]