Locate regex strings with repeats or a sliding window

Asked Jan 03 '19 at 19:34

Active Jan 03 '19 at 19:34

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Given the following:

# 123456789X12345678  # locator numbers for reference
 "TESTHEHEHETESTHEHE"

I would like to locate all positions of the string "HEHE". The desired output would be 5, 7, and 15. The trouble is the immediate "repeat" of "HEHE" after position #5. So if I use stringr::str_locate_all, I get:

stringr::str_locate_all("TESTHEHEHETESTHEHE", "HEHE")
[[1]]
     start end
[1,]     5   8
[2,]    15  18

Which misses the match beginning at position #7.

asked Jan 03 '19 at 19:34

JasonAizkalns

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`str_locate_all("TESTHEHEHETESTHEHE", "(?=HEHE)")` – Wiktor Stribiżew Jan 03 '19 at 19:39
@WiktorStribiżew Wow, that's pretty neat and not how I currently think of positive lookahead. Can you explain why this works? – JasonAizkalns Jan 03 '19 at 19:49
Lookahead check is tried at every location in the string, one by one, from left to right. – Wiktor Stribiżew Jan 03 '19 at 19:54

Locate regex strings with repeats or a sliding window

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