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Posted By

jatkins on 06/26/10


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index substring


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Find the nth occurrence of a substring

 / Published in: Ruby
 

Public domain. Returns the nth occurrence of substring within var, or -1 if var does not include n substrings or if n is negative. Does not account for overlapping substrings (one solution is to delimit substrings, such as with a space, so you can pass " or " as substring to find occurrences of "or" as a word).

See also Find n from the index of the nth occurrence of a substring.

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  1. def find_nth_occurrence(var, substring, n)
  2. 	position = -1
  3. 	if n > 0 && var.include?(substring) # is n positive, and var includes substring
  4. 		i = 0
  5. 		while i < n do
  6. 			position = var.index(substring, position+substring.length) if position != nil
  7. 			i += 1
  8. 		end
  9. 	end
  10. 	return position != nil && position != -1 ? position + 1 : -1; # return the index of the nth occurrence of substring if it exists, otherwise -1
  11. end

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