Cumulative sums for the previous row

Question

I'm trying to get cumulative sums for the previous row/year. Running cumsum(data$fonds) gives me the running totals of adjacent sells, which doesn't work for what I want to do. I would like to have my data look like the following:

   year      fond   cumsum  
1  1950       0       0  
2  1951       1       0
3  1952       3       1
4  1953       0       4
5  1954       0       4

Any help would be appreciated.

Answer 1

data$cumsum <- c(0, cumsum(data$fonds)[-nrow(data)])