R: Group adjacent object in vector

Question

I've a big vector of 200,000 objects. The vector contains integers values. And the vector is sorted. How can I split the vector in chunk of adjacent points.

Example :

x <- c(1,4,5,6,8,9,20,21,30)

Will give me (here a R list as a result) :

[[1]]
[1] 1

[[2]]
[1] 4 5 6

[[3]]
[1] 8 9

[[4]]
[1] 20 21

[[5]]
[1] 30

The basic way would be to loop across the values but it's not very efficient. Any ideas ?

All values in the vector are integers. To be adjacent values have to be at a distance of 1 frome each other. Example : 2 and 3 — Nicolas Rosewick, Apr 10 '17 at 08:58

score 1 · Accepted Answer · answered Apr 10 '17 at 08:58

1

We can use diff with cumsum to create a grouping variable and split the vector

unname(split(x, cumsum(c(TRUE, diff(x)!=1))))
#[[1]]
#[1] 1

#[[2]]
#[1] 4 5 6

#[[3]]
#[1] 8 9

#[[4]]
#[1] 20 21

#[[5]]
#[1] 30

answered Apr 10 '17 at 08:58

akrun

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R: Group adjacent object in vector

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