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

[Nordlund, Dan (DSHS/RDA)]

> -----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]
> 

Sorry for the noise.  That should have been

v[-length(v)] + v[-1]


Hope this is more helpful,

Dan

Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204