R help - Dec 2007 - Efficient way to find consecutive integers in vector?

Hi all,

Does anybody have a magic trick handy to isolate directly consecutive
integers from something like this:
c(1,2,3,4,7,8,9,10,12,13)

The result should be, that groups 1-4, 7-10 and 12-13 are consecutive
integers ...

Thanks for any hints, Joh

Joh,

x <- c(1,2,3,4,7,8,9,10,12,13)
which(diff(x) != 1)

gives the indices of the 'jumps'.

Gabor

On Thu, Dec 20, 2007 at 10:43:05PM +0100, Johannes Graumann
wrote:
> Hi all,
> 
> Does anybody have a magic trick handy to isolate directly consecutive
> integers from something like this:
> c(1,2,3,4,7,8,9,10,12,13)
> 
> The result should be, that groups 1-4, 7-10 and 12-13 are consecutive
> integers ...
> 
> Thanks for any hints, Joh
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
-- 
Csardi Gabor <csardi at rmki.kfki.hu>    MTA RMKI, ELTE TTK

On Thu, 2007-12-20 at 22:43 +0100, Johannes Graumann
wrote:
> Hi all,
> 
> Does anybody have a magic trick handy to isolate directly consecutive
> integers from something like this:
> c(1,2,3,4,7,8,9,10,12,13)
> 
> The result should be, that groups 1-4, 7-10 and 12-13 are consecutive
> integers ...
> 
> Thanks for any hints, Joh
Not fully tested, but here is one possible approach:
> Vec
 [1]  1  2  3  4  7  8  9 10 12 13

Breaks <- c(0, which(diff(Vec) != 1), length(Vec))
> Breaks
[1]  0  4  8 10
> sapply(seq(length(Breaks) - 1), 
         function(i) Vec[(Breaks[i] + 1):Breaks[i+1]])
[[1]]
[1] 1 2 3 4

[[2]]
[1]  7  8  9 10

[[3]]
[1] 12 13



For a quick test, I tried it on another vector:


set.seed(1)
Vec <- sort(sample(20, 15))
> Vec
 [1]  1  2  3  4  5  6  8  9 10 11 14 15 16 19 20

Breaks <- c(0, which(diff(Vec) != 1), length(Vec))
> Breaks
[1]  0  6 10 13 15
> sapply(seq(length(Breaks) - 1), 
         function(i) Vec[(Breaks[i] + 1):Breaks[i+1]])
[[1]]
[1] 1 2 3 4 5 6

[[2]]
[1]  8  9 10 11

[[3]]
[1] 14 15 16

[[4]]
[1] 19 20


HTH,

Marc Schwartz

Thanks for your Inputs!

Joh

Johannes Graumann wrote:
> Hi all,
> 
> Does anybody have a magic trick handy to isolate directly consecutive
> integers from something like this:
> c(1,2,3,4,7,8,9,10,12,13)
> 
> The result should be, that groups 1-4, 7-10 and 12-13 are consecutive
> integers ...
> 
> Thanks for any hints, Joh
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html and provide commented,
> minimal, self-contained, reproducible code.