How can I refer to actual (n) and previous (n-1) elements in a vector?

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Nordlund, Dan (DSHS/RDA)
Sent: Monday, December 06, 2010 9:21 AM
To: r-help at r-project.org
Subject: Re: [R] How can I refer to actual (n) and previous (n-1)
elements in a vector?

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Marianne Stephan
Sent: Monday, December 06, 2010 9:13 AM
To: r-help at r-project.org
Subject: [R] How can I refer to actual (n) and previous (n-1)

elements

in a vector?


Hello,


How can I apply a function on a vector that refers to actual (n) and
previous elements in the vector (e.g. n-1)?


For example:
I would like to calculate the sum of (n-1) + n for each element of a
vector and get a vector as a result.


Besides others I tried this:


v<-c(3,6,8,1,1,3,9,5,6,3)
for (i in 1:NROW(v)){a[i]<-a[i-1]+a[i]}


I would like to get this result:
9,14,9,2,4,12,14,11,9


I would greatly appreciate your help!
Marianne
	[[alternative HTML version deleted]]

How about something like

v[-n] +  v[-1]