Array join function - Ruby on Rails

I wrote below function to return unique years (with unrepeated digits) in a range of years. My results turned out to be fine, however, the spec requires a certain format which my join function returned array of string instead of numbers. How do I convert the end result to an array of numbers as spec required?

def no_repeat?(year)
  idx = 1
  str = year.to_s
  while idx < str.length
    if str[0] == str[idx]
      return false
    end
    idx += 1
  end
  return true
end

def no_repeats(year_start, year_end)
  diff = year_end - year_start
  idx = 0
  new = []
  while idx <= diff
    year = year_start + idx
    if no_repeat?(year)
      new.push(year.to_i)
    end
    idx += 1
  end
  return [new.join(",")]
end

Test Results:

#no_repeats                                                                                                                                                                            
  should return a no repeat year (FAILED - 1)                                                                                                                                          
  should not return a repeat year (FAILED - 2)                                                                                                                                         
  should return only those years that have no repeated digits (FAILED - 3)                                                                                                             

Failures:                                                                                                                                                                              

  1) #no_repeats should return a no repeat year                                                                                                                                        
     Failure/Error: no_repeats(1234, 1234).should == [1234]                                                                                                                            
       expected: [1234]                                                                                                                                                                
            got: ["1234"] (using ==)                                                                                                                                                   
     # ./spec/01_no_repeats_spec.rb:16:in `block (2 levels) in <top (required)>'                                                                                                       

  2) #no_repeats should not return a repeat year                                                                                                                                       
     Failure/Error: no_repeats(1123, 1123).should == []                                                                                                                                
       expected: []                                                                                                                                                                    
            got: [""] (using ==)                                                                                                                                                       
     # ./spec/01_no_repeats_spec.rb:20:in `block (2 levels) in <top (required)>'                                                                                                       

  3) #no_repeats should return only those years that have no repeated digits                                                                                                           
     Failure/Error: ]                                                                                                                                                                  
       expected: [1980, 1982, 1983, 1984, 1985, 1986, 1987]                                                                                                                            
            got: ["1980,1982,1983,1984,1985,1986,1987"] (using ==)                                                                                                                     
     # ./spec/01_no_repeats_spec.rb:32:in `block (2 levels) in <top (required)>'   
Finished in 0.00139 seconds                                                                                                                                                            
3 examples, 3 failures                                                                                                                                                                 

Failed examples:                                                                                                                                                                       

rspec ./spec/01_no_repeats_spec.rb:15 # #no_repeats should return a no repeat year                                                                                                     
rspec ./spec/01_no_repeats_spec.rb:19 # #no_repeats should not return a repeat year                                                                                                    
rspec ./spec/01_no_repeats_spec.rb:23 # #no_repeats should return only those years that have no repeated digits