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

Question

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 seaching 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

Answer 1

require 'enumerator' # Needed in 1.8.6 only
"1#3#a#".enum_for(:scan,/#/).map { Regexp.last_match.begin(0) }
#=> [1, 3, 5]

ETA: This works by creating an Enumerator that uses scan(/#/) as its each method.

scan yields each occurence of the specified pattern (in this case /#/) and inside the block you can call Regexp.last_match to access the MatchData object for the match.

MatchData#begin(0) returns the index where the match begins and since we used map on the enumerator, we get an array of those indices back.

Answer 2

s = "a#asg#sdfg#d##"
a = (0 .. s.length - 1).find_all { |i| s[i,1] == '#' }

Answer 3

here's a long method chain:

"a#asg#sdfg#d##".
    each_char.
    each_with_index.
    inject([]) {|indices, (char, idx)| indices << idx if char == "#"; indices}
# => [1, 5, 10, 12, 13]

requires 1.8.7+

Answer 4

Here's a less-fancy way:

i = -1
all = []
while i = x.index('#',i+1)
  all << i
end
all

In a quick speed test this was about 3.3x faster than FM's find_all method, and about 2.5x faster than sepp2k's enum_for method.

Answer 5

annother solution derived from FM's answer:

s = "a#asg#sdfg#d##"
q = []
s.length.times {|i| q << i if s[i,1] == '#'}

I love that Ruby never has only one way of doing something!