R help - Apr 2007 - sequences extraction

Hello,

I need to extract sequences from an ordered vector.
For example, if
a<-c(1,2,3,6,10,11,13)
I need to get the followings 4 vectors 
(1,2,3),(6),(10,11),(13)

Thank You
-Bruno


------------------------------------------------------
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Hi,
> I need to extract sequences from an ordered vector.
> For example, if
> a<-c(1,2,3,6,10,11,13)
> I need to get the followings 4 vectors 
> (1,2,3),(6),(10,11),(13)
There should be a more elegant way to do it, but the following code
seems to work (it returns the results a s a list) :


a<-c(9,1,2,3,6,10,11,17,13,14)
d <- diff(a)
result <- list()
tmp <- a[1]            
for (i in 1:length(d)) {  
        if (d[i]==1) {
                tmp <- c(tmp, a[i+1])
        } else {
                result <- c(result,list(tmp))
                tmp <- a[i+1]         
        }
}
result <- c(result,list(tmp))   
result


Hope that helps,

Julien

-- 
Julien Barnier
Groupe de recherche sur la socialisation
ENS-LSH - Lyon, France

Here is one way of doing it:
> a
[1]  1  2  3  6 10 11 13
> b <- c(FALSE, diff(a) != 1)
> cumsum(b)
[1] 0 0 0 1 2 2 3
> split(a, cumsum(b))
$`0`
[1] 1 2 3

$`1`
[1] 6

$`2`
[1] 10 11

$`3`
[1] 13
>

On 4/20/07, Bruno C. <bruno.c at inwind.it> wrote:
> Hello,
>
> I need to extract sequences from an ordered vector.
> For example, if
> a<-c(1,2,3,6,10,11,13)
> I need to get the followings 4 vectors
> (1,2,3),(6),(10,11),(13)
>
> Thank You
> -Bruno
>
>
> ------------------------------------------------------
> Leggi GRATIS le tue mail con il telefonino i-mode? di Wind
> http://i-mode.wind.it/
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
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http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

Here's a solution which uses diff() and apply.

findSequences <- function(Data){
     # Sort the vector in case it hasn't been sorted
     Data <- sort(Data)
     # Check that there are no duplicate values in Data
     if(any(duplicated(Data))) stop("Function with not work if Data
argument contains duplicate values.")
     # Make a matrix of the starting and ending indices of sequences
     Breaks <- which(diff(Data) != 1)
     Starts <- c(0, Breaks) + 1
     Ends <- c(Breaks, length(Data)) 
     SequenceIndices <- cbind(Starts, Ends)
     # Return a list of vectors of sequences
     apply(SequenceIndices, 1, function(x) Data[x[1]:x[2]])
     }
>> I need to extract sequences from an ordered vector.
>> For example, if
>> a<-c(1,2,3,6,10,11,13)
>> I need to get the followings 4 vectors 
>> (1,2,3),(6),(10,11),(13)
>There should be a more elegant way to do it, but the following code
>seems to work (it returns the results a s a list) :
>a<-c(9,1,2,3,6,10,11,17,13,14)
>d <- diff(a)
>result <- list()
>tmp <- a[1]            
>for (i in 1:length(d)) {  
>        if (d[i]==1) {
>                tmp <- c(tmp, a[i+1])
>        } else {
>                result <- c(result,list(tmp))
>                tmp <- a[i+1]         
>        }
>}
>result <- c(result,list(tmp))   
>result

Brian Gregor, P.E.
Transportation Planning Analysis Unit
Oregon Department of Transportation
Brian.J.GREGOR at odot.state.or.us
(503) 986-4120