Explanation for try ruby

gistfile1.rb

➜  ~  irb
 :001 > books = {}
 :002 > books[:one] = :good
 :003 > books[:two] = :bad
 :004 > books[:three] = :good
 => :good
 :012 > books
 => {:one=>:good, :two=>:bad, :three=>:good}
 :005 > ratings = Hash.new(0) # Here is important magic! Default value for hash is zero, usually it is nil
 => {}
 :006 > ratings[:any] # let's try random call for hash
 => 0 # It returns default value 0
 :007 > # Let's check step by step "books.values.each {|rate| ratings[rate] += 1}"

 :008 > books.values
 => [:good, :bad, :good]

.each{|rate|  action } 
means iterate through iteratable and store value in variable rate
block will be caleld 3 times, values of rate inside block will be [:good, :bad, :good]

# first time rate equals :good
 :009 > ratings[:good] # let's check default value of ratings[:good]
 => 0  # it's zero because of special Hash

  # a +=1 is the same like a = a + 1
 :010 > ratings[:good] = ratings[:good] + 1
 # is equals to ratings[:good] = 0 + 1
 => 1
 :011 > ratings[:good] # is now equals 1

# let's run and see the result
 :014 > books.values.each { |rate| ratings[rate] += 1 }
 => [:good, :bad, :good] # return books.values, but made some action on ratings[rate]
 :015 > ratings # now collects count of different hash values
 => {:good=>2, :bad=>1}