Recursively add consecutive vector values in R

Question

Assume I have a vector containing the following values:

foo <- c(1:5)
[1] 1 2 3 4 5 

Is there a function or otherwise quick way to get each value of foo to add recursively to the numbers before it?

Desired Result is a vector containing these added values:

1 3 6 10 15

• foo[1] is 1, foo[1] + foo[2] is 1 + 2 = 3, foo[1] + foo[2] + foo[3] is 1 + 2 + 3 = 6, etc.

My attempt:

I came up with:

vapply(1:length(foo), function(x) sum(foo[1]:foo[x]),integer(1))

But I'm hoping there is a simpler way to do this...

Answer 1

Yes, cumsum does exactly that:

cumsum(foo)
# [1]  1  3  6 10 15

Another handy and closely related function is cumprod(x) for cumulative products. See ?cumsum.