Is there a way to vectorize operations that access multiple elements of a vector?

Question

Let's say I have a vector of integers:

> a<-sample(1:100,10)  
> a  
 [1] 13 23 97 70 63 32 82 31 15 36  

And I want a vector containing the cumulative values of this vector. That is, I want the vector
13 36 133 203 266 298 380 411 426 462

One way to achieve this would be to use a for loop. I prefer doing it using apply/lapply/sapply/..., but the only way I can think of for doing this is:

sapply(1:length(a), function(x) {sum(a[1:x])})
[1]  13  36 133 203 266 298 380 411 426 462

This works, but I was wondering if there was a better way to do this. Is there?
(This may have been a bad example, but in general, is there a way to access elements of the list being iterated over, given that you know the position of these element relative to the current one?)

Answer 1

You may giggle, but there's already a built in function for this, see ?cumsum

x <- sample(1:100,20)
x

 [1] 32 42 54 79 92 69 96 41 51 22 74 76 86 37 85 99  3 11 17 57

cumsum(x)

 [1]   32   74  128  207  299  368  464  505  556  578  652  728  814  851  936
[16] 1035 1038 1049 1066 1123