delete near duplicated row

library(data.table)
library(magrittr)
DT <- fread('
id click
1  a
1  a
1  b
1  a
1  c
1  c
1  a
1  a
1  b
1  b
1  b
1  a
2  a
2  a
2  b
2  c
2  a
2  b
2  c')

indx <- DT %$% paste0(id, click) %>% rle %$%
  cumsum(c(1, lengths)) %>% .[1:(length(.)-1)]
DT[indx, ]
#     id click
#  1:  1     a
#  2:  1     b
#  3:  1     a
#  4:  1     c
#  5:  1     a
#  6:  1     b
#  7:  1     a
#  8:  2     a
#  9:  2     b
# 10:  2     c
# 11:  2     a
# 12:  2     b
# 13:  2     c