I'm not sure whether this is what you want

a = c(1:10)
a/sum(a) # percentage
cumsum(a)/sum(a) #cumulative percentage

好像不对啊,为什么分母是 sum(a) 呢?
What if the data is like this:
a <- data.frame(sample(1:100,20),rnorm(20),rnorm(20))

How could you get the cumulative percent for each variable in the data frame?

cumsum(percent)