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

A slight improvement over your each_with_index.map line

arr.map.with_index {|a, i| a == 'x' ? i : nil}.compact # => [0, 2, 6]