count_unique_values.rb

# Getting a list of unique values and their counts in Ruby

languages = ["Ruby", "PHP", "Ruby", "Ruby", "Shell", "PHP", "Ruby", nil, "VimL", "Ruby", "Ruby", "PowerShell", "JavaScript", nil, nil, "PowerShell", "CSS", nil, nil, "Ruby", "PowerShell", "Ruby", "VimL"]

########## The ugly way ##########
hash = Hash.new(0)
languages.each do |language|
  hash[language] += 1
end
counts = hash
########## end The ugly way ##########


########## The cool, hip, ruby way ##########
# Iterate over each member of the languages array, and increment the value of the key in the hash
#  - Pass a new hash into the iteration, and setting a default value of 0, more info here: http://www.ruby-doc.org/core-2.0.0/Hash.html#method-c-new
#  - Pass two variables to the block, `hash` and `language` where `hash` == `Hash.new(0)`, and `language` == the current iteration of the array
#  - Increment the value of the hash where it's key is equal to `language`. For example, hash["Ruby"] is incremented by one when it's in that iteration
#  - Return the hash when done
counts = languages.inject(Hash.new(0)) {|hash,language| hash[language] += 1; hash}
########## end The cool, hip, ruby way ##########

puts counts
# => {"Ruby"=>8, "PHP"=>2, "Shell"=>1, nil=>5, "VimL"=>2, "PowerShell"=>3, "JavaScript"=>1, "CSS"=>1}

# And if you want it sorted: (more info on how this works, here: http://www.ruby-doc.org/core-2.0.0/Hash.html#method-c-5B-5D)
puts ordered_counts = Hash[counts.sort_by {|k,v| v}.reverse]
# => {"Ruby"=>8, nil=>5, "PowerShell"=>3, "VimL"=>2, "PHP"=>2, "Shell"=>1, "JavaScript"=>1, "CSS"=>1}