How can I count runs in a sequence?
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
Use rle()
:
y <- rle(c(1,0,0,0,1,0,0,0,0,0,2,0,0))
y$lengths[y$values==0]
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))