I would like to efficiently find the first index of each unique value in a very large vector.
For example, if I have a vector A<-c(9,2,9,5) I would like to return not only the unique values (2,5,9) but also their first indices (2,4,1). I tried using a for loop with which(A==unique(A)[i])[1] to find the first index of each unique value but it is very slow. What I am trying to do is easily and quickly done with the "unique" function in MATLAB (see http://www.mathworks.com/help/techdoc/ref/unique.html). Thank you for your help, Bronwyn [[alternative HTML version deleted]] ______________________________________________ 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.
