Get prevvious value of a column and create vector of cumsum

Question

I have following R code:

>a
 1
 2
 3
 4
 5

I want to create b such that b[i] = a[i] + b[i-1].

Need help, how to do above action in R.

Answer 1

b <- cumsum(b) + a

wil do the trick.

Answer 2

Like this?

Rgames> a <- 1:5
Rgames> b<-rep(7,5)
Rgames> b[-1]<-b[1:(length(b)-1)]+a[1:(length(a)-1)]
Rgames> b
[1]  7  8  9 10 11

You haven't stated whether you expect to add the updated value of b[j-1] to the new value of b[j] .