Vfrdtyky

I was creating a ruby programme that will calculate the frequency of each letter appearing in my text and will be return it as a Hash.

Below is my code:

class LetterHistogram

  attr_reader :letters

  attr_accessor :text



  def initialize(t = "Hello World!")

    @text = t

  end



  def display

    calculateFrequencies

    ("A".."Z").each {|x| puts "#{x}: " + "*" * letters[x]}

  end



  private

  attr_writer :letters



  def calculateFrequencies

    calcuFreq = String.new(text)

    calcuFreq.upcase!.gsub!(/W+/, '')

    letters.clear

    letters.default = 0

    calcuFreq.each_char {|char| letters[char] += 1}

  end

end

But I getting this error when I run the display method
enter image description here

What is the error means and how to solve it?

The main problem is that in calculateFrequencies you are using a not assigned variable: letters. So, when you call calculateFrequencies in display, letters = nil and calling .clear on nil returns the error.

This is a modified version of the code, using snake_case (which is the Ruby writing standard).

class LetterHistogram

  attr_accessor :text



  def initialize(t = "Hello World!")

    @text = t

  end



  def display

    calculate_frequencies.each { |letter, freq| puts "#{letter}: #{freq}"}

  end



  private



  def calculate_frequencies

    freq = @text.upcase.gsub!(/W+/, '').each_char.with_object(Hash.new(0)) { |letter, freq| freq[letter] += 1 }

    freq.sort_by{ |letter, freq| freq }.reverse # just to sort

  end

end

Instantiating an object and calling .display on it:

senctence = LetterHistogram.new

senctence.display



#=> L: 3 

#=> O: 2 

#=> D: 1 

#=> R: 1 

#=> W: 1 

#=> E: 1 

#=> H: 1 

How it works

For calculating the frequency I used a Hash populated by: https://ruby-doc.org/core-2.5.1/Enumerable.html#method-i-each_with_object

Printing out freq from calculate_frequencies you can see it:

#=> {"H"=>1, "E"=>1, "L"=>3, "O"=>2, "W"=>1, "R"=>1, "D"=>1}

freq = ("A".."Z").each_with_object({}) { |letter, freq| freq[letter] = 0 }

"Hello World!".upcase.gsub!(/W+/, '').each_char { |letter| freq[letter] += 1 }



#=> {"A"=>0, "B"=>0, "C"=>0, "D"=>1, "E"=>1, "F"=>0, "G"=>0, "H"=>1, "I"=>0, "J"=>0, "K"=>0, "L"=>3, "M"=>0, "N"=>0, "O"=>2, "P"=>0, "Q"=>0, "R"=>1, "S"=>0, "T"=>0, "U"=>0, "V"=>0, "W"=>1, "X"=>0, "Y"=>0, "Z"=>0}

Finally, to print out the istogram:

freq.each { |letter, freq| puts "#{letter}: " + "◼︎" * freq if freq > 0 }



#=> D: ◼︎

#=> E: ◼︎

#=> H: ◼︎

#=> L: ◼︎◼︎◼︎

#=> O: ◼︎◼︎

#=> R: ◼︎

#=> W: ◼︎