Question

Input : [1,2,2,3,4,2]

Output : Index of 2 = [1,2,5]

Answer 1

A method like this:

def indexes_of_occurrence(ary, occ)
  indexes = []
  ary.each_with_index do |item, i|
    if item == occ
      indexes << i
    end
  end
  return indexes
end

Gives you the following:

irb(main):048:0> indexes_for_occurrence(a, 2)
=> [1, 2, 5]
irb(main):049:0> indexes_for_occurrence(a, 1)
=> [0]
irb(main):050:0> indexes_for_occurrence(a, 7)
=> []

I’m sure there’s a way to do it a one liner (there always seems to be!) but this’ll do the job.