Find indices of elements that match a given condition

Question

Given an array, how can I find all indices of elements those match a given condition?

For example, if I have:

arr = [\'x\', \'o\', \'x\', \'.\', \'.\         


        

Answer 1

Ruby 1.9:

arr = ['x', 'o', 'x', '.', '.', 'o', 'x']
p arr.each_index.select{|i| arr[i] == 'x'} # =>[0, 2, 6]

Code