R help - Aug 2012 - splitting a vector

Hello,

I have a vector with positive integer numbers, e.g. 
> numbers <- c(1,2,1,2,3,4,5)
and want to split the vector whenever an element in the vector is smaller or
equal to its predecessor. 
Hence I want to obtain two vectors: c(1,2) and c(1,2,3,4,5).
I tried with which(), but it is not so elegant:
> numbers[1:(which(numbers<=numbers[1])[2]-1)]
> numbers[which(numbers<=numbers[1])[2]:length(numbers)]
Sure I can do it with a for-loop, but that seems a bit tedious for that
small problem. 
Does maybe anyone know a simple and elegant solution for this? I'm searching
for a general solution, since
my vector may change and maybe be split into more than two vectors, e.g.
give five vectors for c(1,1,2,3,4,5,1,2,3,2,3,4,5,6,4,5).

Many thanks in advance,

Hannes







--
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Hello,

Try the following.


fun <- function(x){
     n.diff <- cumsum(diff(c(x[1], x)) <= 0)
     split(x, n.diff)
}

numbers <- c(1,2,1,2,3,4,5)
fun(numbers)

fun(  c(1,1,2,3,4,5,1,2,3,2,3,4,5,6,4,5) )

Hope this helps,

Rui Barradas
Em 01-08-2012 14:29, capy_bara escreveu:
> Hello,
>
> I have a vector with positive integer numbers, e.g.
>
>> numbers <- c(1,2,1,2,3,4,5)
> and want to split the vector whenever an element in the vector is smaller
or
> equal to its predecessor.
> Hence I want to obtain two vectors: c(1,2) and c(1,2,3,4,5).
> I tried with which(), but it is not so elegant:
>
>> numbers[1:(which(numbers<=numbers[1])[2]-1)]
>> numbers[which(numbers<=numbers[1])[2]:length(numbers)]
> Sure I can do it with a for-loop, but that seems a bit tedious for that
> small problem.
> Does maybe anyone know a simple and elegant solution for this? I'm
searching
> for a general solution, since
> my vector may change and maybe be split into more than two vectors, e.g.
> give five vectors for c(1,1,2,3,4,5,1,2,3,2,3,4,5,6,4,5).
>
> Many thanks in advance,
>
> Hannes
>
>
>
>
>
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/splitting-a-vector-tp4638675.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.

The following 'f' counts the number of times the sequence x
does not increase.  Is this what you want?
> f <- function(x) split(x, cumsum(c(TRUE, x[-1] <= x[-length(x)])))
> f(numbers)
$`1`
[1] 1 2

$`2`
[1] 1 2 3 4 5
> f(c(1,1,2,3,4,5,1,2,3,2,3,4,5,6,4,5))
$`1`
[1] 1

$`2`
[1] 1 2 3 4 5

$`3`
[1] 1 2 3

$`4`
[1] 2 3 4 5 6

$`5`
[1] 4 5


Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org] On Behalf
> Of capy_bara
> Sent: Wednesday, August 01, 2012 6:30 AM
> To: r-help at r-project.org
> Subject: [R] splitting a vector
> 
> Hello,
> 
> I have a vector with positive integer numbers, e.g.
> 
> > numbers <- c(1,2,1,2,3,4,5)
> 
> and want to split the vector whenever an element in the vector is smaller
or
> equal to its predecessor.
> Hence I want to obtain two vectors: c(1,2) and c(1,2,3,4,5).
> I tried with which(), but it is not so elegant:
> 
> > numbers[1:(which(numbers<=numbers[1])[2]-1)]
> > numbers[which(numbers<=numbers[1])[2]:length(numbers)]
> 
> Sure I can do it with a for-loop, but that seems a bit tedious for that
> small problem.
> Does maybe anyone know a simple and elegant solution for this? I'm
searching
> for a general solution, since
> my vector may change and maybe be split into more than two vectors, e.g.
> give five vectors for c(1,1,2,3,4,5,1,2,3,2,3,4,5,6,4,5).
> 
> Many thanks in advance,
> 
> Hannes
> 
> 
> 
> 
> 
> 
> 
> --
> View this message in context:
http://r.789695.n4.nabble.com/splitting-a-vector-
> tp4638675.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> 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.

I come up with:

runs <- function(numbers) {
     tmp <- diff(c(0, which(diff(numbers) <= 0), length(numbers)))
     split(numbers, rep(seq_along(tmp), tmp))
}



Can't say it's elegant, but it seems to work
> runs(c(1:3, 1:4))
$`1`
[1] 1 2 3

$`2`
[1] 1 2 3 4
> runs(c(1,1,1))
$`1`
[1] 1

$`2`
[1] 1

$`3`
[1] 1
> runs(c(1:3, 2:3, 3))
$`1`
[1] 1 2 3

$`2`
[1] 2 3

$`3`
[1] 3


HTH,

Jan



capy_bara <hettling at few.vu.nl> schreef:
> Hello,
>
> I have a vector with positive integer numbers, e.g.
>
>> numbers <- c(1,2,1,2,3,4,5)
>
> and want to split the vector whenever an element in the vector is smaller
or
> equal to its predecessor.
> Hence I want to obtain two vectors: c(1,2) and c(1,2,3,4,5).
> I tried with which(), but it is not so elegant:
>
>> numbers[1:(which(numbers<=numbers[1])[2]-1)]
>> numbers[which(numbers<=numbers[1])[2]:length(numbers)]
>
> Sure I can do it with a for-loop, but that seems a bit tedious for that
> small problem.
> Does maybe anyone know a simple and elegant solution for this? I'm
searching
> for a general solution, since
> my vector may change and maybe be split into more than two vectors, e.g.
> give five vectors for c(1,1,2,3,4,5,1,2,3,2,3,4,5,6,4,5).
>
> Many thanks in advance,
>
> Hannes
>
>
>
>
>
>
>
> --
> View this message in context:  
> http://r.789695.n4.nabble.com/splitting-a-vector-tp4638675.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.