How to show unique strings in Rails? - ruby-on-rails

Question

I want to categorise Companies by letters in my listing page.
But there are multiple records that start with the same letter. I can get the first letters of Company names with the .first method.
But my code shows duplicate letters.
Controller:
#brand = Brand.where(slug: params[:brand]).first
#companies = Company.where(brand_id: #brand.id)....
View:
<% #companies.each do |c| %>
<li>
<%= link_to company_path(c.brand.name,c.id) do %>
<%= c.name.first %>
<% end %>
</li>
<% end %>
How would I show only unique letters?

Answer 1

New code (with some changes, assuming company belongs_to brand and brand has_many companies)
#brand = Brand.where(slug: params[:brand]).first
#companies = #brand.companies
##list is a hash with letters as keys and an array of companies starting with this letter
#list = Hash.new { |h,k| h[k]=[] }
#companies.each { |comp| #list[comp.name[0]] << comp }
#As “engineersmnky” suggested on a comment the last two sentences can be simplified:
#list = #companies.group_by { |c| c.name[0] }
View:
<% #list.each do |letter, companies| %>
<h2><%= letter %><h2>
<% companies.each do |c| %>
<li>
<%= link_to c.name, c %>
</li>
<% end %>
<% end %>

Answer 2

You're iterating through all companies so if you have companies like, Facebook and Foxtel, a link with F tag is going to be duplicated. You can do something like
categories = #companies.where(brand_id: #brand.id).pluck(:name).map(&:first).uniq
In the above code all it is doing is getting a list of company names and extracting out the first letter and removing the duplicates.
Now you can iterate through the categories and create a link for the category and inside the category page you can get companies starting from that letter
Company.where('name LIKE ?', "%#{starting_character}%")
starting_character gets sent from the list of categories page.