得到不同数据的值:

%w(a b c a c d).uniq

得到各个元素出现的个数:

count_hash = {}
%w(a b c a c d).each do |item|
  key = item.to_sym
  if count = count_hash[key]
    count_hash[key] = count + 1
  else
    count_hash[key] = 1
  end
end

str='a,b,c,a,c,d'

counter = Hash.new(0)

str.split(',').each { |val| counter[val]+=1 }

puts counter