How to check if a vector contains n consecutive numbers

Question

Suppose that my vector numbers contains c(1,2,3,5,7,8), and I wish to find if it contains 3 consecutive numbers, which in this case, are 1,2,3.

numbers = c(1,2,3,5,7,8) difference = diff(numbers) //The difference output would be 1,1,2,2,1 

To verify that there are 3 consecutive integers in my numbers vector, I've tried the following with little reward.

rep(1,2)%in%difference  

The above code works in this case, but if my difference vector = (1,2,2,2,1), it would still return TRUE even though the "1"s are not consecutive.

Answer 1

Using diff and rle, something like this should work:

result <- rle(diff(numbers)) any(result$lengths>=2 & result$values==1) # [1] TRUE 

In response to the comments below, my previous answer was specifically only testing for runs of length==3 excluding longer lengths. Changing the == to >= fixes this. It also works for runs involving negative numbers:

> numbers4 <- c(-2, -1, 0, 5, 7, 8) > result <- rle(diff(numbers4)) > any(result$lengths>=2 & result$values==1) [1] TRUE