How can I count runs in a sequence?

Asked 2009-10-01T09:32:31.900

In R, what would be the most efficient/simplest way to count runs of identical elements in a sequence?

For example, how to count the numbers of consecutive zeros in a sequence of non-negative integers:

x <- c(1,0,0,0,1,0,0,0,0,0,2,0,0) # should give 3,5,2

r count

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1 Answer

This can be done in an efficient way by using indexes of where the values change:

x <- c(1,0,0,0,1,2,1,0,0,1,1)

Find where the values change:

diffs <- x[-1L] != x[-length(x)]

Get the indexes, and then get the difference in subsequent indexes:

idx <- c(which(diffs), length(x))
diff(c(0, idx))

answered 2009-10-01T11:16:44.253