Q:

elsif a letter contained in an array

How would I basically say within the elsif below "if letter == (a letter contained within the array "letterbank") ===> print letter"
def hide_or_not(an_array, a_guess)
    an_array.each do |letter|
      if a_guess == letter
        print a_guess
      elsif SOMETHING HERE
        print letter
      else
        print "_"
      end
    end
  end

assuming the method is fed a_guess which is a letter in string form and an array of single letters.  When a letter is guessed, it appears, or else a "_" is printed
an_array = ["r", "i", "c", "s", "h", "a", "w"]
letter_guess = "r"

then sorry I also assuming I have to save each letter guessed so I want to somewhere inlcude a letterbank. I don't know if I should do that below the moethod or within it... (already guessed letters)
letterbank = ["s", "w", "t", "j"]

so in this case, I would want the below to print... thanks!
r___s__w

A:

This solution is using a string instead of array but can just as easily use arrays. (Adding the chars to a string and printing after completing the iteration gives some extra flexibility in the printing for example allowing you to use puts). 
class LetterGuesser # Hangman
  def initialize(word) 
    @word = word;
    @guessed_letters = '';
  end

  def guess_letter(letter)
    @guessed_letters << letter if !@guessed_letters.include?(letter)
    current_guesses = ''
    @word.each_char do |char| 
      if guessed_letters.include?(char) 
        current_guesses << letter 
      else
        current_guesses << '_' 
      end
    end
    puts current_guesses
  end
end

game = LetterGuesser.new('test')
game.guess_letter('e')

