Identify position range values within a vector

Question

I was wondering if there would be the possibility to identify the position of the range values according to a condition. This condition is determined by the longest sequence of values lower than 3.

For instance,

x <- c(4, 1, 2, 1, 1, 4, 1, 1, 1, 1, 2, 1, 1, 1, 1, 4, 1, 1)

Desired output:

c(7:15)

It may be that split() and rle() could be useful in this case but any help will be more than helpful.

Answer 1

You could do the rle on x < 3, then find which of the TRUEs is max. Then sum the lengths before the match plus one as well as the match itself (which will be the final position). Finally do a sequence with the values.

rl <- rle(x < 3)
w <- which(rl$lengths == max(rl$lengths) & rl$values)
do.call(seq.int, list(sum(rl$lengths[1:(w - 1)]) + 1, sum(rl$lengths[1:w])))
# [1]  7  8  9 10 11 12 13 14 15