Efficient way to find repeated runs of rows, remove, & count

Question

I have a data set with repeating rows. I want to remove consecutive repeated and count them but only if they're consecutive. I'm looking for an efficient way to do this. Can't think of how in dplyr or data.table.

MWE

dat <- data.frame(     x = c(6, 2, 3, 3, 3, 1, 1, 6, 5, 5, 6, 6, 5, 4),     y = c(7, 5, 7, 7, 7, 5, 5, 7, 1, 2, 7, 7, 1, 7),     z = c(rep(LETTERS[1:2], each=7)) )  ##        x     y     z ## 1      6     7     A ## 2      2     5     A ## 3      3     7     A ## 4      3     7     A ## 5      3     7     A ## 6      1     5     A ## 7      1     5     A ## 8      6     7     B ## 9      5     1     B ## 10     5     2     B ## 11     6     7     B ## 12     6     7     B ## 13     5     1     B ## 14     4     7     B 

Desired output

       x     y     z   n 1      6     7     A   1 2      2     5     A   1 3      3     7     A   3 4      1     5     A   2 5      6     7     B   1 6      5     1     B   1 7      5     2     B   1 8      6     7     B   2 9      5     1     B   1  10     4     7     B   1 

Answer 1

With data.table:

library(data.table) setDT(dat)  dat[, c(.SD[1L], .N), by=.(g = rleidv(dat))][, g := NULL]      x y z N  1: 6 7 A 1  2: 2 5 A 1  3: 3 7 A 3  4: 1 5 A 2  5: 6 7 B 1  6: 5 1 B 1  7: 5 2 B 1  8: 6 7 B 2  9: 5 1 B 1 10: 4 7 B 1