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  1. string <- "Junk1_Junk2_Junk3__ID1_Junk4_Junk5.pdf"
  2. library(stringr)
  3. stringr::str_extract(string, "[^_]+(?=(?:_[^_]*){2}$)")
  4.  
  5. ## Base R:
  6. sub(".*?([^_]+)(?:_[^_]*){2}$", "\\1", string)
Success #stdin #stdout 0.27s 42212KB
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[1] "ID1"
[1] "ID1"
https://ideone.com/RlMsmL
language:
R (R 3.5.2)
created:
4 years ago
visibility:
public

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