Finding groups of contiguous numbers in a list [du

Question

This question already has an answer here:

• Sequence length encoding using R 6 answers

This is a duplicate question to this, except for R rather than Python.

I'd like to identify groups of contiguous (some people call them continuous) integers in a list, where duplicate entries are treated as existing within the same range. Therefore:

myfunc(c(2, 3, 4, 4, 5, 12, 13, 14, 15, 16, 17, 17, 20))

returns:

min  max
2    5
12   17
20   20

Although any output format would be fine. My current brute-force, for-loop method is pretty slow.

(Apologies if I could have easily re-interpreted the Python answer and I'm being stupid!)

Answer 1

Just use diff:

x = c(2, 3, 4, 4, 5, 12, 13, 14, 15, 16, 17, 17, 20)

start = c(1, which(diff(x) != 1 & diff(x) != 0) + 1)
end = c(start - 1, length(x))

x[start]
# 2 12 20
x[end]
# 5 17 20