cumsum list..

Hi all, i have the following.. 

a <- data.frame(data = seq(1,10))

i have indices:
x <- c(1, 5, 3, 9)
y <- c(2, 7, 4, 10)

I want the cumsum of a[1:2], a[5:7], a[3:4]... 

is there an elegant way to do it without any loop? Thanks!

View this message in context: http://www.nabble.com/cumsum-list..-tp16025202p16025202.html
Sent from the R help mailing list archive at Nabble.com.