Return index of all occurrences of a character in a string in ruby

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I am trying to return the index's to all occurrences of a specific character in a string using Ruby. A example string is "a#asg#sdfg#d##" and the expected return is [1,5,10,12,13] when searching for # characters. The following code does the job but there must be a simpler way of doing this?

def occurances (line)

  index = 0
  all_index = []

  line.each_byte do |x|
    if x == '#'[0] then
      all_index << index
    end
    index += 1
  end

  all_index
end
ruby string
6 Answers

Here's a solution for massive strings. I'm doing text finds on 4.5MB text strings and the other solutions grind to a halt. This takes advantage of the fact that ruby .split is very efficient compared to string comparisions.

def indices_of_matches(str, target)
      cuts = (str + (target.hash.to_s.gsub(target,''))).split(target)[0..-2]
      indicies = []
      loc = 0
      cuts.each do |cut|
        loc = loc + cut.size
        indicies << loc
        loc = loc + target.size
      end
      return indicies
    end

It's basically using the horsepower behind the .split method, then using the separate parts and the length of the searched string to work out locations. I've gone from 30 seconds using various methods to instantaneous on extremely large strings.

I'm sure there's a better way to do it, but:

(str + (target.hash.to_s.gsub(target,'')))

adds something to the end of the string in case the target is at the end (and the way split works), but have to also make sure that the "random" addition doesn't contain the target itself.

indices_of_matches("a#asg#sdfg#d##","#")
=> [1, 5, 10, 12, 13]
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