vector indexing

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Hi,

Is it what you're looking for?

which(y>4)  ##all indexes for y>4
[1]  3  6  7  9 11
which(y>4)[1]  ##the first index
[1] 3

HTH,
Ivan

--
Ivan CALANDRA
Universit? de Bourgogne
UMR CNRS/uB 6282 Biog?osciences
6 Boulevard Gabriel
21000 Dijon, FRANCE
+33(0)3.80.39.63.06
ivan.calandra at u-bourgogne.fr
http://biogeosciences.u-bourgogne.fr/calandra

Le 23/10/12 11:21, Al Ehan a ?crit :
Hi,

I got a small problem on how to define the vector index without manually
inspect the vector.

example:

y=c(2,3,5,2,4,6,8,3,6,2,5) #I have ten set of this kind of vectors (with
different values but same length) that I would also like to run the routine
below

#say;
v=the first index in y where the value is larger than 4, in this case index
3, value 5

#what I would like to do is take y[1:v] and run it to some function
#hence I should also get y[(v+1),length(y)] and can run to other function
as well..

I know this is easy peasy for you..please help, many thanks.

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Hello,

Try the following.

y=c(2,3,5,2,4,6,8,3,6,2,5)

first <- function(x) min(which(x))
prefix <- function(x, v) x[seq_len(v)]
suffix <- function(x, v) x[-seq_len(v)]

first(y > 4)
prefix(y, first(y > 4))
suffix(y, first(y > 4))

Hope this helps,

Rui Barradas
Em 23-10-2012 10:21, Al Ehan escreveu:
Hi,

I got a small problem on how to define the vector index without manually
inspect the vector.

example:

y=c(2,3,5,2,4,6,8,3,6,2,5) #I have ten set of this kind of vectors (with
different values but same length) that I would also like to run the routine
below

#say;
v=the first index in y where the value is larger than 4, in this case index
3, value 5

#what I would like to do is take y[1:v] and run it to some function
#hence I should also get y[(v+1),length(y)] and can run to other function
as well..

I know this is easy peasy for you..please help, many thanks.

	[[alternative HTML version deleted]]

______________________________________________
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.
Hello,

Try the following.

y=c(2,3,5,2,4,6,8,3,6,2,5)

first <- function(x) min(which(x))
prefix <- function(x, v) x[seq_len(v)]
suffix <- function(x, v) x[-seq_len(v)]

first(y > 4)
prefix(y, first(y > 4))
suffix(y, first(y > 4))

Be careful with this:  it fails if the condition is FALSE for every 
element, e.g.

 > first(y > 10)
[1] Inf
Warning message:
In min(which(x)) : no non-missing arguments to min; returning Inf

I don't know if this is possible in the original context, or what the 
desired result would be if it happens:  but it's something to look out for.

Duncan Murdoch