map(&:to_i)すると文字列は0として評価される

[4] pry(main)> array = Array[1,2,3,'user_id']
=> [1, 2, 3, "user_id"]
[8] pry(main)> sorted_array = array.map(&:to_i)
=> [1, 2, 3, 0]
[9] pry(main)> sorted_array = array.map(&:to_i).uniq
=> [1, 2, 3, 0]
[10] pry(main)> sorted_array = array.map(&:to_i).uniq.select{ |i| i > 0 }
=> [1, 2, 3]
[11] pry(main)> sorted_array = array.map(&:to_i).uniq.select{ |i| i > 0 }.sort
=> [1, 2, 3]