R - conditional incrementation

Question

This should be trivial to code but could not think of an elegant one-liner in R. I have a dataframe as below:

data <- data.frame( index= seq(1:20), event=rep(0,20)   )
data$event[10] <- 1
data$event[15] <- 1

I simply want to add start and stop counter columns that increment in 10's and reset right after an event=1 is observed. So the desired output with these two additional columns would be:

  index event start stop
1   1    0     0    10
2   2    0    10    20
3   3    0    20    30
4   4    0    30    40
5   5    0    40    50
6   6    0    50    60
7   7    0    60    70
8   8    0    70    80
9   9    0    80    90
10  10   1    90    100
11  11   0    0     10
12  12   0    10    20
13  13   0    20    30
14  14   0    30    40
15  15   1    40    50
16  16   0    0     10
17  17   0    10    20
18  18   0    20    30
19  19   0    30    40
20  20   0    40    50

Obviously, data$stop <- data$start + 10 but how can I apply() the start incrementation loigc as described?

Answer 1

How about this:

Reduce(function(x,y) (1-y)*(x+10), data$event[-nrow(data)], accumulate=T, init=0)