Assign unique IDs by group, according to pattern

Question

I have a grouped dataset, but the groups don\'t have a unique identifier, like this:

direction <- c(\'N\',\'S\',\'W\',\'N\',\'N\',\'S\',\'W\',\'N\',\'S\',\'W\         


        

Answer 1

I think this should work:

direction <- c('N','S','W','N','N','S','W','N','S','W')
measurement <- c(4,6,1,7,2,4,7,4,1,4)
x <- data.frame(direction, measurement)

inds <- which(direction == 'N')
diffs <- diff(c(inds, length(direction)+1))

groups <- rep(seq_along(inds),diffs)

x$ID <- LETTERS[groups]
x

Note that if you have more than 26 groups, LETTERS[] will start returning NA. You can always just use:

x$ID <- groups

If that happens.