How to calculate the highest word frequency in Ruby - ruby-on-rails

Question

I have been working on this assignment for a Coursera Intro to Rails course. We have been tasked to write a program that calculates maximum word frequency in a text file. We have been instructed to create a method which:
Calculates the maximum number of times a single word appears in the given content and store in highest_wf_count.
Identify the words that were used the maximum number of times and store that in highest_wf_words.
When I run the rspec tests that were given to us, one test is failing. I printed my output to see what the problem is but haven't been able to fix it.
Here is my code, the rspec test, and what I get:
class LineAnalyzer
attr_accessor :highest_wf_count
attr_accessor :highest_wf_words
attr_accessor :content
attr_accessor :line_number
def initialize(content, line_number)
#content = content
#line_number = line_number
#highest_wf_count = 0
#highest_wf_words = highest_wf_words
calculate_word_frequency
end
def calculate_word_frequency()
#highest_wf_words = Hash.new(0)
#content.split.each do |word|
#highest_wf_words[word.downcase!] += 1
if #highest_wf_words.has_key?(word)
#highest_wf_words[word] += 1
else
#highest_wf_words[word] = 1
end
#highest_wf_words.sort_by{|word, count| count}
#highest_wf_count = #highest_wf_words.max_by {|word, count| count}
end
end
def highest_wf_count()
p #highest_wf_count
end
end
This is the rspec code:
require 'rspec'
describe LineAnalyzer do
subject(:lineAnalyzer) { LineAnalyzer.new("test", 1) }
it "has accessor for highest_wf_count" do
is_expected.to respond_to(:highest_wf_count)
end
it "has accessor for highest_wf_words" do
is_expected.to respond_to(:highest_wf_words)
end
it "has accessor for content" do
is_expected.to respond_to(:content)
end
it "has accessor for line_number" do
is_expected.to respond_to(:line_number)
end
it "has method calculate_word_frequency" do
is_expected.to respond_to(:calculate_word_frequency)
end
context "attributes and values" do
it "has attributes content and line_number" do
is_expected.to have_attributes(content: "test", line_number: 1)
end
it "content attribute should have value \"test\"" do
expect(lineAnalyzer.content).to eq("test")
end
it "line_number attribute should have value 1" do
expect(lineAnalyzer.line_number).to eq(1)
end
end
it "calls calculate_word_frequency when created" do
expect_any_instance_of(LineAnalyzer).to receive(:calculate_word_frequency)
LineAnalyzer.new("", 1)
end
context "#calculate_word_frequency" do
subject(:lineAnalyzer) { LineAnalyzer.new("This is a really really really cool cool you you you", 2) }
it "highest_wf_count value is 3" do
expect(lineAnalyzer.highest_wf_count).to eq(3)
end
it "highest_wf_words will include \"really\" and \"you\"" do
expect(lineAnalyzer.highest_wf_words).to include 'really', 'you'
end
it "content attribute will have value \"This is a really really really cool cool you you you\"" do
expect(lineAnalyzer.content).to eq("This is a really really really cool cool you you you")
end
it "line_number attribute will have value 2" do
expect(lineAnalyzer.line_number).to eq(2)
end
end
end
This is the rspec output:
13 examples, 1 failure
Failed examples:
rspec ./course01/module02/assignment-Calc-Max-Word-Freq/spec/line_analyzer_spec.rb:42 # LineAnalyzer#calculate_word_frequency highest_wf_count value is 3
My output:
#<LineAnalyzer:0x00007fc7f9018858 #content="This is a really really really cool cool you you you", #line_number=2, #highest_wf_count=[nil, 10], #highest_wf_words={"this"=>2, nil=>10, "is"=>1, "a"=>1, "really"=>3, "cool"=>2, "you"=>3}>
Based on the test string, the word counts aren't correct.
"nil" is being included in the hash.
The hash is not being sorted by the value (count) like it should.
I tried several things to fix these problems and nothing has worked. I went through the lecture material again, but can't find anything that would help and the discussion boards are not often monitored for questions from students.

Answer 1

Accoriding to Ruby documentation:
downcase!(*args) public
Downcases the contents of str, returning nil if no changes were made.
Due to this unexpected behavior of .downcase! method, if the word is already all lowercase, you're incrementing occurrences of nil in this line:
#highest_wf_words[word.downcase!] += 1
Tests are also failing because #highest_wf_words.max_by {|word, count| count} returns an array containing the count and a word, while we want to get only the count.
A simplified calculate_word_frequency method passing the tests would look like this:
def calculate_word_frequency()
#highest_wf_words = Hash.new(0)
#content.split.each do |word|
# we don't have to check if the word existed before
# because we set 0 as default value in #highest_wf_words hash
# use .downcase instead of .downcase!
#highest_wf_words[word.downcase] += 1
# extract only the count, and then get the max
#highest_wf_count = #highest_wf_words.map {|word, count| count}.max
end
end

Answer 2

Nil:
The nil is from downcase!
This modifies the String inplace and returns nil if nothing has changed.
If you say "this is weird", then you are right (IMHO).
# just use the non destructive variant
word.downcase
Sorting:
sort_by returns a new object (Hash, Array, ...) and does not modify the receiver of the method. You either need to re-assign or to use sort_by!
unsorted = [3, 1, 2]
sorted = unsorted.sort
p unsorted # => [3, 1, 2]
p sorted # => [1, 2, 3]
unsorted.sort!
p unsorted # => [1, 2, 3]
Faulty word count:
Once you corrected those two mistakes it should look better. Be aware, that the method does not return a single integer but a two-element array with the word and count, so it should look something like this: ["really", 6]
Simplifiying things:
If you can use ruby 2.7, then there is the handy Enumerable#tally method!
%w(foo foo bar foo baz foo).tally
=> {"foo"=>4, "bar"=>1, "baz"=>1}
Example taken from
https://medium.com/#baweaver/ruby-2-7-enumerable-tally-a706a5fb11ea