In R, how can I make a running count of runs?

Question

Suppose I have an R dataframe that looks like this, where end.group signifies the end of a unique group of observations:

x <- data.frame(end.group=c(0,0,1,0,0,1,1,0,0,0,1,1,1,0,1))

I want to return the following, where group.count is a running count of the number of observations in a group, and group is a unique identifier for each group, in number order. Can anyone help me with a piece of R code to do this?

end.group group.count group
0         1           1
0         2           1
1         3           1
0         1           2
0         2           2
1         3           2
1         1           3
0         1           4
0         2           4
0         3           4
1         4           4
1         1           5
1         1           6
0         1           7
1         2           7

Answer 1

You can create group by using cumsum and rev . You need rev because you have the end points of the groups.

x <- data.frame(end.group=c(0,0,1,0,0,1,1,0,0,0,1,1,1,0,1))
# create groups
x$group <- rev(cumsum(rev(x$end.group)))
# re-number groups from smallest to largest
x$group <- abs(x$group-max(x$group)-1)

Now you can use ave to create group.count .

x$group.count <- ave(x$end.group, x$group, FUN=seq_along)

Answer 2

x <- data.frame(end.group=c(0,0,1,0,0,1,1,0,0,0,1,1,1,0,1))

ends <- which(as.logical(x$end.group))
ends2 <- c(ends[1],diff(ends))
transform(x, group.count=unlist(sapply(ends2,seq)), group=rep(seq(length(ends)),times=ends2))
   end.group group.count group
1          0           1     1
2          0           2     1
3          1           3     1
4          0           1     2
5          0           2     2
6          1           3     2
7          1           1     3
8          0           1     4
9          0           2     4
10         0           3     4
11         1           4     4
12         1           1     5
13         1           1     6
14         0           1     7
15         1           2     7