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

Question

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").

Answer 1

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

with(rle(x), rep(ifelse(lengths == 1, "no", "yes"), lengths))

# [1] "yes" "yes" "no"  "no"  "yes" "yes"

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

with(rle(x), rep(lengths != 1, lengths))

# [1]  TRUE  TRUE FALSE FALSE  TRUE  TRUE