ruby - How to join nested char array to string -

i have following code:

def caesar_cipher(text, move_by)     move_by %= 26     chars = hash[('a'..'z').map.with_index.to_a]     converted = text.split.map |word|         word.chars.map |char|             if (chars[char.downcase] + move_by) <= 26                 chars.key(chars[char.downcase] + move_by)             else                 chars.key(chars[char.downcase] + move_by - 26)             end         end     end end  print caesar_cipher("what string", 5) 

it converts string variable text integer. here output when run it: [["b", "m", "f", "y"], ["f"], ["x", "y", "w", "n", "s", "l"]], , i'd joined this"bmft f xywnsl". i've tried .join method, gives me "bmftfxywnsl"

if:

arr = [["b", "m", "f", "y"], ["f"], ["x", "y", "w", "n", "s", "l"]] 

then

arr.map(&:join).join(' ')   #=> "bmfy f xywnsl"  

you can think of map(&:join) as:

arr.map { |a| a.join }.join(' ') 

isn't ruby great?