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  1. x <- c("aaaaaaah" ,"aaaah","ahhhh","cooee","helloee","mmmm","noooo","ohhhh","oooaaah","ooooh","sshh","ummmmm","vroomm","whoopee","yippee")
  2. grep(".*([a-z])\\1.*(?!\\1)([a-z])\\2", x, value=TRUE, perl=TRUE)
Success #stdin #stdout 0.24s 39404KB
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Standard input is empty
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[1] "cooee"   "helloee" "oooaaah" "sshh"    "vroomm"  "whoopee" "yippee"
https://ideone.com/ulgRXq
language:
R (R 3.5.2)
created:
4 years ago
visibility:
public

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