How to match a value in a vector with the one before and after in r?

  • A+

I'm trying to identify mismatched values based on one element value before or after the focal value in a vector. Any thought about how to do it?

Let's say, I have a vector: x<-c(1,1,2,1,3,3). If element[i] matches with the element before or after item i (element[i-1] and element[i+1]). If there is a match element[i] should equal "yes", otherwise it should equal "no".

The expected output for x<-c(1,1,2,1,3,3) should be c("yes","yes","no","no","yes","yes").


Use rle() to identify runs of equal values. rle(x)$length == 1 means there is no equal values before or after the current one.

rep(ifelse((len <- rle(x)$lengths) == 1, "no", "yes"), len) # [1] "yes" "yes" "no"  "no"  "yes" "yes" 

Edit: more concise version(thanks for @dww's comment)

rep((len <- rle(x)$lengths) == 1, len) # [1] FALSE FALSE  TRUE  TRUE FALSE FALSE 


:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen: