Remove/collapse consecutive duplicate values in sequence

Question

I have the following dataframe:

a a a b c c d e a a b b b e e d d

The required result should be

a b c d e a b e d         


        

Answer 1

library(dplyr)
x <- c("a", "a", "a", "b", "c", "c", "d", "e", "a", "a", "b", "b", "b", "e", "e", "d", "d")
x[x!=lag(x, default=1)]
#[1] "a" "b" "c" "d" "e" "a" "b" "e" "d"

EDIT: For data.frame

  mydf <- data.frame(
    V1 = c("a", "a", "a", "b", "c", "c", "d", "e", 
         "a", "a", "b", "b", "e", "e", "d", "d"),
    V2 = c(1, 2, 3, 2, 4, 1, 3, 9, 
         4, 8, 10, 199, 2, 5, 4, 10),
   stringsAsFactors=FALSE)

dplyr solution is one liner:

mydf %>% filter(V1!= lag(V1, default="1"))
#  V1 V2
#1  a  1
#2  b  2
#3  c  4
#4  d  3
#5  e  9
#6  a  4
#7  b 10
#8  e  2
#9  d  4

post scriptum

lead(x,1) suggested by @Carl Witthoft iterates in reverse order.

leadit<-function(x) x!=lead(x, default="what")
rows <- leadit(mydf[ ,1])
mydf[rows, ]

#   V1  V2
#3   a   3
#4   b   2
#6   c   1
#7   d   3
#8   e   9
#10  a   8
#12  b 199
#14  e   5
#16  d  10